Objectives. - The objective of this study was to analyse how depression influences sexual desires and activities of gay men to understand the co-occurrence of depressed mood, high sex drive and unprotected anal intercourse with casual partners (UAIC) among some individuals. Methods. - In 2004, French gay men visiting a major gay Internet site participated in an online survey assessing serological status, numbers of casual partners, sex drive and control over sex drive, UAIC, depression and its impact on sexual desire. Results. - One thousand nine hundred (and) thirty-two men who had casual partners in the previous year were included in the analysis. HIV-negative men on average had 22 casual partners per annum, and 28% reported UAIC. Insertive UAIC was practised with 4.5 partners, and receptive UAIC with 4 partners. Sexual activity and risk-taking were substantially higher for HIV-positive men (M = 46 partners, 58% UAIC), and HIV+ men had UAIC with more partners (insertive M = 20, receptive M = 22). Whereas depression lowered sexual desire among most gay men, a minority of men (22%) experienced the reverse effect. HIV+ men more often reported that depression strongly increased their sexual desires. These depressive sexual urges were found to increase sexual activity and reduce men's control over their sex drive. The combined effects of depressed sexual urges, high level of sex-drive, and low control over sex drive, explained 34% of the variance in risk behaviour in HIV-negative men and 56% of the variance in risk behaviour in HIV-positive men. Discussion. - In some gay men, especially those who are HIV-positive, sexual activity seems to be seems to be used to cope with depressive moods. Sexual coping however significantly increases exposures to risk because it may result in sexual compulsivity and reduces the amount of control individuals have over their sex drive. Tackling the issue of mental health amongst gay men is therefore an important challenge for the prevention of HIV. (c) 2006 Elsevier SAS. Tous droits reserves.