Objective:To assess whether the custom of prolonged post-partum sexual abstinence in Benin is associated with an increased incidence of extra-marital sexual contacts by husbands.Design:Cross-sectional survey of adult men and women.Methods:Data obtained from men on their extra-marital sexual behaviour in the past 12 months were linked to data on post-partum abstinence over the same time interval reported by wives. Multivariate analysis was applied to assess the association between conjugal abstinence and husband′s extra-marital sex, net of the effects of possible confounders.Results:Approximately half of married men experienced post-partum abstinence in the past 12 months. In this group, 32% reported one or more extra-marital sexual contacts compared with 20% among those who experienced no abstinence (OR=1.8,P<0.001). This association is essentially unchanged after controlling for marriage type, age, education, urban-rural residence, income and household wealth. Age, income and wealth are also significant predictors of the probability of extra-marital sex. The effects of income and wealth largely disappear when attention is restricted to extra-marital sex without using a condom on the most recent occasion.Conclusions:The potentially protective effect of prolonged abstinence after childbirth in Benin (and probably in much of West Africa) is offset by an increased probability that husbands will seek extra-marital partners without using condoms. Although not quantifiable, the enhanced longer-term risks of sexually transmitted diseases/HIV infection for wives probably outweigh the short-term benefits. Family planning practitioners in this region should not hesitate to recommend the early resumption of sex and suitable methods of post-partum contraception for women who express concern or uncertainty about their husband′s behaviour.