In two Copenhagen University hospitals 12,885 pregnant women, seen during the period 1.8.1992 to 30.04.1995, answered questionnaires regarding consumption of alcohol, tobacco, cannabis and other drugs. The prevalence of cannabis use was 0.8%. Women using cannabis but no other illicit drugs were each retrospectively matched with four randomly chosen pregnant women in the same period and the same age group and with same parity. Eighty-four cannabis users were included. These women were socioeconomically disadvantaged and had a higher prevalence of present and past use of alcohol, tobacco and other drugs. No significant difference in pregnancy, delivery or puerperal outcome was found. Children of women using cannabis were 150 g lighter, 1.2 cm shorter and had 0.2 cm smaller head circumference than the control infants. Controlling for the child's sex and maternal use of alcohol did not eliminate the significant differences in birthweight and length; however, they were eliminated by controlling for maternal tobacco smoking. It is concluded, that the use of cannabis is not a major prognostic factor regarding the outcome of pregnancy, but is an indicator of low socioeconomic status and use of other substances.