Besen has interviewed hundreds of former and current "ex-gays", and is an outspoken critic of organizations such as Homosexuals Anonymous.
In September 2000, Besen photographed ex-gay activist John Paulk, then Chairman of Exodus International, in a Washington D.C. gay bar called Mr. P's. Paulk said he was simply there to use the washroom, but Besen and other witnesses allege he was drinking and flirting for over 20 minutes. Besen went public with the story, and wrote about it in his book Anything But Straight: Unmasking the Scandals and Lies Behind the Ex-Gay Myth. The book was nominated for two Lambda Literary Awards in 2003.
Besen's photograph of Paulk in September 2000 (and the subsequent release of the story) was instrumental in the ultimate removal of Paulk as Chairman of Exodus International. Exodus International was a major organization in the "Ex-gay movement" until it was disbanded in June 2013. As noted by The Washington Post in October 2002, "John Paulk had been the most famous success story of the Christian ex-gay movement, which seeks to persuade gay men and lesbians to accept Jesus and renounce homosexuality. He had appeared on 60 Minutes, Oprah and the cover of Newsweek."
In June 2013, Exodus International reversed its positions on reparative therapy, apologized to the gay community for the "trauma" and "hurt" the organization had wreaked on them, and disbanded the organization. Besen reflected: