Objectives of the study were to assess the differences between sexes in the likelihood of starting antiretroviral therapy (ART), in rates of sustained discontinuation from highly active antiretroviral therapy (HAART), and in clinical progression. In a multicenter cohort study (I.Co.N.A. Study), 2323 men and 1335 women previously naive to antiretrovirals were enrolled. As of September 2002, 807 women and 1480 men started ART. The median time to starting ART was 28 weeks for women and 17 weeks for men (P = 0.0003 by log-rank test). This difference was no longer significant after adjusting for either HIV RNA (P = 0.21) or CD4 count (P = 0.28) at enrollment. Women tend to start HAART less frequently than mono/dual ART after adjusting for potential confounders (odds ratio = 0.78, 95% confidence interval [CI]: 0.60-1.01; P = 0.06). Women who started HAART were 1.4 times more likely than men (95% CI: 1.00-1.99; P = 0.05) to interrupt at least 1 drug because of toxicity. Twenty-one percent of women and 19% of men interrupted HAART altogether for more than 3 months (P = 0.3). Clinical progression was observed in 53 women (22.6%) and 137 men (23.4%; P = 0.56). Risk of developing a clinical event was found to be no different between women and men (relative hazard = 0.84, 95% CI: 0.56-1.26; P = 0.40).