Usaam Auf Mukwaaya was one of three people arrested for a peaceful protest at the HIV/AIDS Implementers' Meeting last month.
The International Gay and Lesbian Human Rights Commission (IGLHRC) said in a statement today:
"Mr Mukwaaya was on his way back from Friday prayers (on July 25th) when he was stopped by a police patrol car.
"Three men in police uniform and a fourth in civilian attire put Mr Mukwaaya in the patrol car.
"He was driven to a building where he was led through a dark hall to an interrogation room, and aggressively questioned about the Ugandan LGBT movement.
"Mr Mukwaaya was cut around the hands and tortured with a machine that applies extreme pressure to the body, preventing breathing and causing severe pain.
"Sexual Minorities Uganda (SMUG), a coalition of three LGBTI organisations in Uganda, and the IGLHRC, searched unsuccessfully for Mr Mukwaaya from 3:00pm on July 25 to the morning of July 26, 2008, inquiring as to his whereabouts at five police stations in Kampala.
"On July 26, 2008, at about 11:40am, Mr Mukwaaya was driven from the building where he'd been held for about 30 to 45 minutes and dumped.
"Shaken and bruised, he boarded a motorbike taxi to the city centre and telephoned colleagues from SMUG who found him weak, filthy and without shoes and some of his clothing."
IGLHRC has called on people to send faxes and emails in protest at Mr Mukwaaya's treatment to the President of Uganda, Kaguta Yoweri Museveni, and other officials.
The Ugandan President spoke of his country's "rejection" of homosexuality during a speech he gave at the wedding of a former MP's daughter earlier this month.
Mr Museveni said the purpose of life was to create children and that homosexuality was a "negative foreign culture."
During his time in office LGBT Ugandans have been repeatedly threatened, harassed or attacked. Many have fled the country.
The plight of Uganda's gay men and lesbians has been highlighted recently, with high profile asylum cases such as Prossy Kakooza championed by Peter Tatchell and LGBT equality groups.
Many gay asylum seekers are being deported from the UK on the premise that they can continue to pursue their sexuality in the native land if they act "discreetly."
The IGLHRC said:
"In the past five years, the government has arrested LGBT people on sodomy charges, harassed LGBT human rights defenders, and fined a private radio station that broadcast programming on HIV prevention and men who have sex with men," the group said.
"In July 2005, Uganda's Parliament passed an amendment to the constitution making Uganda only the second country in the world to use its constitution to outlaw marriage between people of the same sex.
"A coalition of religious leaders has marched through the streets of Kampala demanding the arrests of LGBT people with one cleric even calling for the "starving to death" of homosexuals.
"Inspired by the official homophobia of the state, the Ugandan media has published lists of gay men and lesbians, leading to physical violence, loss of employment and educational opportunities by LGBT people."