This study reports the use of psychotropic drugs and pregnancy outcome in a prospective survey carried out in northern Finland in 1985-1986, consisting of 7933 pregnant women and their 8030 births. Of the mothers, 120 (1.5%) used psychotropic drugs during pregnancy and of them 26 (0.3% of the total) used these drugs before and during the pregnancy. According to the logistic regression analysis, the biological and social background variables associating significantly with the use of these drugs were maternal advanced age and multiparity (> 35 years and > 4 parous), overweight (body mass index > the 90th percentile), smoking, alcohol use, belonging to social class IV, and failure to ensure contraception. The users needed hospital observation significantly more often during pregnancy (regular users, 80.8%; occasional users, 38.3; nonusers, 27.4%) and the adjustment of the background variables did not change this result. Of the pregnancy complications bleeding was significantly more common among users than nonusers (23.3 vs. 13.2%) and this difference was not explained by difference in background variables. The mean birth weight of infants of the regular users was significantly lower (255 g) when background variables were standardized by linear regression analysis. No association of increased number of birth defects was found with usage of psychotropic drugs.