Condoms must be used effectively in order to prevent pregnancy and the spread of HIV/STD. This study investigated two types of ineffective condom use, delayed condom use (initiated after penetration has occurred) and condom slippage and/or breakage. We estimated prevalence and identified predictors of ineffective condom use among young women at risk of STDs. The study used baseline survey data from a randomized trial of women 18-24 years old at two managed care sites; 779 participants who were recent condom users were included in this analysis. Forty-four per cent of the sample reported delayed condom use in the past three months and 19% reported condom slippage and/or breakage. In multivariate logistic regression, younger age, primary partner, lack of partner support, multiple recent sexual partners and using condoms for contraception were positively associated with delayed condom use. Correlates of condom slippage and/or breakage were non-white race/ethnicity and history of any STD. Greater frequency of condom use independently predicted both outcomes. Ineffective condom use was common in this sample of experienced condom users and predictors were different for each outcome. HIV/STD prevention interventions must address more specific aspects of condom use than have previously been their focus, especially when condom use is already high.