Dunham was having a pool party with some of her HBO co-stars like Allison Williams, as they continue to film the sixth and final season.
"Mother bleeping pool party at the Hilton Garden Inn," she said. "Say hi guys! The pool party rages on."
She also took a bikini selfie in her black and pink two piece on Instagram Stories, writing, "When the Target swimsuit does a b**ch right, Endo scars & all."
Dunham has opened up in the past about her struggle with Endometriosis. In November 2015, she penned an essay about the disease on her site Lenny Letter.
See more photos of Lena Dunham through the years:
NEW YORK, NY - FEBRUARY 02: Lena Dunham discusses Let Girls Learn at The American Magazine Media Conference at Grand Hyatt New York on February 2, 2016 in New York City. (Photo by Gary Gershoff/WireImage)
PARK CITY, UT - JANUARY 24: Actress Lena Dunham speaks from the podium at the Lena Dunham and Planned Parenthood Host Sex, Politics & Film Cocktail Reception at The Spur on January 24, 2016 in Park City, Utah. (Photo by Nicholas Hunt/Getty Images)
NEW YORK, NY - APRIL 24: Honoree Lena Dunham speaks onstage at Variety's Power of Women New York presented by Lifetime at Cipriani 42nd Street on April 24, 2015 in New York City. (Photo by Brian Ach/Getty Images for Variety)
WEST HOLLYWOOD, CA - JANUARY 13: Actress Lena Dunham attends ELLE's Annual Women in Television Celebration on January 13, 2015 at Sunset Tower in West Hollywood, California. Presented by Hearts on Fire and Olay. (Photo by Michael Buckner/Getty Images for ELLE)
BEVERLY HILLS, CA - JANUARY 11: Actress Lena Dunham attends HBO's post Golden Globe Awards party at The Beverly Hilton Hotel on January 11, 2015 in Beverly Hills, California. (Photo by Jason LaVeris/FilmMagic)
BEVERLY HILLS, CA - JANUARY 11: Actress/director Lena Dunham (L) and singer/songwriter Taylor Swift attend HBO's Official Golden Globe Awards After Party at The Beverly Hilton Hotel on January 11, 2015 in Beverly Hills, California. (Photo by Jeff Kravitz/FilmMagic)
NEW YORK, NY - JANUARY 05: Lena Dunham attends the 'Girls' season four premiere at American Museum of Natural History on January 5, 2015 in New York City. (Photo by Kevin Mazur/WireImage)
NEW YORK, NY - DECEMBER 02: Actress/Author Lena Dunham reads from her book, 'Not That Kind of Girl' during the 2014 Ally Coalition's Talent Show at New World Stages on December 2, 2014 in New York City. (Photo by Mike Pont/Getty Images)
BEVERLY HILLS, CA - NOVEMBER 11: Actress / Director Lena Dunham attends Pen Center USA's 24th Annual Literary Awards Festival at the Beverly Wilshire Four Seasons Hotel on November 11, 2014 in Beverly Hills, California. (Photo by Paul Archuleta/FilmMagic)
LONDON, ENGLAND - OCTOBER 29: Lena Dunham meets fans and signs copies of her book 'Not That Kind Of Girl' at Waterstones, Piccadilly on October 29, 2014 in London, England. (Photo by Stuart C. Wilson/Getty Images)
LOS ANGELES, CA - OCTOBER 14: Actress Lena Dunham signs copies of 'Not That Kind Of Girl: A Young Woman Tells You What She's 'Learned.' at Barnes & Noble bookstore at The Grove on October 14, 2014 in Los Angeles, California. (Photo by Jason LaVeris/FilmMagic)
NEW YORK, NY - SEPTEMBER 30: Television personality Robin Roberts (L) and actress Lena Dunham tape an interview at 'Good Morning America' at the ABC Times Square Studios on September 30, 2014 in New York City. (Photo by Ray Tamarra/GC Images)
LOS ANGELES, CA - AUGUST 25: Actress Lena Dunham arrives at the 66th Annual Primetime Emmy Awards at Nokia Theatre L.A. Live on August 25, 2014 in Los Angeles, California. (Photo by Jon Kopaloff/FilmMagic)
WEST HOLLYWOOD, CA - AUGUST 23: Actress Lena Dunham attends Variety and Women in Film Emmy Nominee Celebration powered by Samsung Galaxy on August 23, 2014 in West Hollywood, California. (Photo by Alberto E. Rodriguez/Getty Images for Variety)
NEW YORK, NY - MAY 05: [EDITOR'S NOTE: Image has been digitally processed] Lena Dunham attends the 'Charles James: Beyond Fashion' Costume Institute Gala at the Metropolitan Museum of Art on May 5, 2014 in New York City. (Photo by Andrew H. Walker/Getty Images)
NEW YORK, NY - APRIL 23: Director Lena Dunham on the set of 'Girls' on April 23, 2014 in New York City. (Photo by Bobby Bank/GC Images)
NEW YORK, NY - MAY 01: Lena Dunham filming 'Girls' on May 1, 2014 in New York City. (Photo by Steve Sands/GC Images)
NEW YORK, NY - APRIL 07: Lena Dunham attends the 2014 Point Honors New York gala at New York Public Library on April 7, 2014 in New York City. (Photo by Nomi Ellenson/FilmMagic)
NEW YORK, NY - MARCH 18: Lena Dunham visits 'The Tonight Show Starring Jimmy Fallon' at Rockefeller Center on March 18, 2014 in New York City. (Photo by Theo Wargo/NBC/Getty Images for 'The Tonight Show Starring Jimmy Fallon')
NEW YORK, NY - MARCH 27: Actress Lena Dunham attends the Fox Searchlight Pictures' 'Dom Hemingway' screening hosted by The Cinema Society And Links Of London on March 27, 2014 in New York City. (Photo by Jim Spellman/WireImage)
NORTH HOLLYWOOD, CA - MARCH 13: Actress Lena Dunham attends an evening with 'Girls' at Leonard H. Goldenson Theatre on March 13, 2014 in North Hollywood, California. (Photo by Jason LaVeris/FilmMagic)
BEVERLY HILLS, CA - JANUARY 13: Writer/director Lena Dunham poses with Best Actress in a TV Comedy Award in the press room during the 70th Annual Golden Globe Awards held at The Beverly Hilton Hotel on January 13, 2013 in Beverly Hills, California. (Photo by Kevin Winter/Getty Images)
NEW YORK, NY - JANUARY 09: Lena Dunham attends the premiere of 'Girls' season 2 hosted by HBO at NYU Skirball Center on January 9, 2013 in New York City. (Photo by Andrew H. Walker/Getty Images)
Cast member Lena Dunham arrives at the premiere of Universal's 'This Is 40,' December 12, 2012 at Grauman's Chinese Theatre in Hollywood, California. AFP PHOTO / ROBYN BECK (Photo credit should read ROBYN BECK/AFP/Getty Images)
AUSTIN, TX - MARCH 12: Writer/Director/Actress Lena Dunham attends 'Girls' Greenroom Photo Op during the 2012 SXSW Music, Film + Interactive Festival at Paramount Theatre on March 12, 2012 in Austin, Texas. (Photo by Michael Buckner/Getty Images for SXSW)
SANTA MONICA, CA - FEBRUARY 26: Actress/filmmaker Lena Dunham, winner of Best First Screenplay for 'Tiny Furniture,' accepts award onstage during the 2011 Film Independent Spirit Awards at Santa Monica Beach on February 26, 2011 in Santa Monica, California. (Photo by Kevork Djansezian/Getty Images)
"The feeling of stopping a crew of 100 people from doing their jobs is far more stressful than missing Intro to Greek Drama class at a liberal-arts college, but I felt the same sense of hot shame," Dunham wrote of her struggles with the illness. "The kind of shame you feel as someone with an anxiety disorder that plays tricks on them. The kind of shame you feel as a woman showing weakness."
She had a surgery in November, noting that afterward, "I was better than I had been in ten years."