This year's Life Ball took place as the Austrian capital basked in the victory of the bearded drag queen Wurst earlier this month, which has at least temporarily given it a self-image as a hotbed of tolerance.
A partygoer who identified himself as Aaron, covered in glitter and topless but for a pair of nipple pasties, said the victory of Wurst - due to perform her winning power ballad "Rise Like A Phoenix" later in the night - had changed the atmosphere.
"I've been here four times before, but this one is by far the best. Usually we hide ourselves before coming to the ball, but this year we can walk openly," he said.
Skimpy costumes were de rigeur, and guests wearing outfits the organisers' "style police" judged to be exceptional could win half-price admission to the Vienna ball. Tickets are normally distributed by a lottery and cost 160 euros ($220).
"I feel so poorly dressed," joked Clinton, sporting conventional evening wear, in opening remarks.
The Life Ball raised about 2.4 million euros ($3.3 million) last year, much of it donated to the Clinton Health Access Initiative to treat and reduce HIV infections in children.
The event this year is inspired by the 15th-century Hieronymus Bosch triptych "The Garden of Earthly Delights", which depicts hedonistic revellers in its centre panel and the Garden of Eden and hell on either side.
The ball has drawn criticism for using Bosch-like posters featuring a nude transgender model, Carmen Carrera. Photographer David LaChapelle designed two versions, showing Carrera with either male or female genitalia, along with the slogan: "I am Adam - I am Eve - I am me." In response, a vigilante granny has attracted media attention by going around defacing the exposed parts.
Life Ball organiser Gery Keszler said the poster was intended to provoke discussion, not to exploit Wurst's Eurovision victory.
'BRINGING EVERYBODY TOGETHER'
"The goal of the poster was to reach a dialogue, but the reaction was bigger than we thought," Keszler told Reuters. "For one night, Vienna seems like the centre of tolerance because the Life Ball brings everybody together. Not everything in the world is black or white, it is all a spectrum, and we wanted to present that," he said in an interview.
Other celebrity guests include Courtney Love, Kesha, and "Desperate Housewives" actress Marcia Cross.
The annual ball, now in its 22nd year, has grown from a small gay-community event to a celebrity-studded society fixture. Its cost-free venue, the neo-Gothic Vienna city hall, is the first government building to host an AIDS-related event.
Sub-Saharan Africa accounts for over 70 percent of the world's HIV-positive people out of an estimated total of 35 million living with the disease worldwide.
According to the United Nations, 2.3 million contracted new HIV infections in 2012 and 1.6 million people died of AIDS-related illnesses.