The effects of pregnancy on cognition and mood were examined using a repeated-measures design. Nineteen women, average age 33, were tested with a comprehensive neuropsychological battery during their last 2 months of pregnancy and again within 2 months of delivery. Blood samples were obtained from all subjects and assayed for a variety of steroid hormones implicated in cognitive and mood functioning. Most participants also completed several self-report measures of mood. In comparison with performance after delivery, women showed significantly more impairment in aspects of verbal memory during pregnancy and also tended to report more negative mood states. Memory deficits were not explained by mood disturbances. No hormone assayed consistently related to cognitive performance during pregnancy. During pregnancy, higher levels of progesterone (P) were associated with greater mood disturbances and higher levels of dehydroepiandrosterone (DHEA) with better mood. After delivery, testosterone (T) was strongly and consistently associated with greater reported mood disturbances. Our results confirm a peripartal memory deficit, which cannot be explained by the dramatic rise in circulating steroid hormones, or by mood status during pregnancy. Steroidal hormones, namely P, DHEA and T, appear to play a role in mood disturbances during, and after, pregnancy. Studies beginning earlier in pregnancy and continuing for an extended period of time after delivery are needed to confirm and expand these observations.