To estimate the impact of the exposure to spermatozoa on the risk of developing pregnancy-induced hypertension, the duration of sexual cohabitation with the father and the use of contraceptive methods were evaluated among 113 primigravid women with pregnancy-induced hypertension and 109 age- and parity-matched controls. The duration of unprotected sexual cohabitation was approximately 50% shorter in women with pregnancy-induced hypertension (2.3 versus 4.7, P < 0.0001), regardless of the contraceptive method previously used. However, the duration of oral contraception use was similar in cases and controls (22.1 versus 23.4 months). Also, of the total group of women who developed pregnancy-induced hypertension, 85.5% (97) became pregnant during the first 3 months of unprotected sexual intercourse in comparison with 54.1% (59) in the control group (P < 0.0001). Results suggest that the risk of pregnancy-induced hypertension in primigravidae is reduced with duration of sexual cohabitation, and therefore with exposure to paternal spermatozoa. However, the protective effect of exposure is not achieved while using oral contraceptives. Considering the present options for nulliparous women, contraception does not appear to be a viable public health policy to reduce the risk of pregnancy induced hypertension.