The traditional proscription against sex for women during pregnancy, and particularly in the postpartum period, in south-west Nigeria leaves many men without sexual access to their wives for extended periods of time. This practice raises the question whether men abstain or seek other sexual partners. A community-based study was conducted using 3204 married men from randomly selected local government areas of the state. These men had wives who had delivered a baby in the 36 months prior to the study. Information was obtained on their sexual practices before and during pregnancy and the postpartum period. Male sexual networking was not absent outside the pregnancy and the postpartum periods. However, during pregnancy, a higher percentage of men (43·7%) had other partners compared with the period outside pregnancy and postpartum (42·1%). The difference was not significant (p>0·05). Similarly, in the postpartum abstinence period, more men (48%) had other sexual partners when compared with the period outside pregnancy and postpartum (42·1%; p<0·001). Sexual networking with non-regular and multiple partners was also more commonly observed in the postpartum period than in pregnancy (11·9% vs 10·4%; p<0·05). Significantly more rural than urban men had multiple sexual partners when their wife was pregnant (p=0·01) or in postpartum abstinence (p<0·05). Condom use with regular partners was largely absent, and consistent condom use with extramarital partners was very low among urban and rural men (6·3% vs 1·7%). The vast majority of men were having unprotected vaginal sex. Logistic regression analysis showed that polygamous men, those under 30 years in the urban area, and men with low or no education were more likely to have sex with other women when their wife was pregnant. During a wife’s postpartum abstinence period, men in higher status occupations, younger urban men (<49 years), those with more children, the polygamous, and men with a first wife under 40 years in urban area were more likely to have other partners. In light of the heterosexual mode of HIV transmission in Nigeria, there is a dire need to design and implement an intervention programme targeted at married men, which takes into consideration cultural practices. This will hopefully help check the course of the disease in a country thought to be on the verge of an HIV epidemic.