CONTEXT: Oral contraceptives are the most popular form of reversible contraception used in developed countries. Their efficacy depends on how consistently and correctly they are used. METHODS: The incidence of inconsistent pill use was estimated from data from a random sample of 1,234 pill users who participated in a French population-based survey in 2000. Multivariate logistic regressions were used to identify the social, demographic and situational characteristics associated with inconsistent use. RESULTS: Twenty percent of women missed at least one pill during the four weeks prior to the interview, 7% missed two or more pills, and 10% missed at least one pill without using contraceptive backup during subsequent sexual intercourse. Inconsistent pill use was related to situational characteristics that are likely to change over time. The odds of having missed pills were elevated among women whose last intercourse had been with an occasional partner or who had small children. Women who did not have a daily pill-taking routine also had elevated odds of inconsistent use. The likelihood of having missed a pill and not used contraceptive backup was elevated among women who felt they had not been involved in the choice of contraceptive method prescribed by their physician. CONCLUSIONS: Service providers may need to better address women's preferences and needs, to help them choose the contraceptive method that best fits their sexual, emotional.