The study objective was to evaluate the effect of a patient information video during the informed consent process of a perinatal trial. Ninety women, between 19 and 33 weeks gestation, were randomised to receive written information about this perinatal trial and watch an information video or to receive written information only. Participants completed a questionnaire immediately after entry and 2-4 weeks later assessing knowledge of; feelings about the worth of; and willingness for future participation in the perinatal trial. When initially asked, more women who watched the video thought they would consent to the study (chi 2 = 6.3; df = 1; P = 0.01). No differences in knowledge about the perinatal trial were found initially, but 2-4 weeks later more knowledge had been retained by women who had watched the video (chi 2 = 6.7; df = 1; P = 0.01). These results suggest that a patient information video combined with an information sheet may result in greater participation in a research trial and may increase women's knowledge of a specific health problem and related research trial.