ObjectiveMost women have some premenstrual symptoms that may be influenced by diverse environmental factors. The aim of this study was to determine the influence of knowledge about premenstrual syndrome (PMS) in the reports of women and their symptoms.MethodWe studied 86 healthy Mexican women whose highest level of education was sixth grade. Participants were assigned to one of two groups. The experimental group watched a videotape describing PMS and its negative consequences in daily life. The control group watched a videotape describing the menstrual cycle. The Menstrual Distress Questionnaire was administered to all women during the first week after menstruation, after which they were shown their designated videotape, and the questionnaire was administered again after the next menstruation.ResultsIn the control group, there were no significant differences in premenstrual symptoms reported both before and after the women watched the videotape. However, women in the experimental group reported more severe premenstrual symptoms after watching the videotape.ConclusionsThese results suggest that after observing the videotape, women's expectancies of negative symptoms in the premenstrual phase increased. Thus, the symptoms reported by these women were enhanced.