The purpose of this study was to determine the prevalence of perimenstrual symptoms (PMS) in a free-living population of US women and to determine if prevalence estimates varied with parity, contraceptive status, characteristics of the menstrual cycle, and selected demographic variables. We identified all households from a census listing for five southeastern city neighborhoods that offered variation in racial composition and socioeconomic status. We ascertained all households in which there was one nonpregnant woman between the ages of 18 and 35 years per household. Of the 241 eligible women, 179 (74 per cent) participated in the study. Trained interviewers administered the Moos Menstrual Distress Questionnaire (MDQ) and other demographic measures to women between March and July 1979. Symptoms with a prevalence greater than 30 per cent included weight gain, headache, skin disorders, cramps, anxiety, backache, fatigue, painful breasts, irritability, mood swings, depression, or tension. Only 2 to 8 per cent of women found most of these severe or disabling. The exceptions were severe cramps reported by 17 per cent of women and severe premenstrual and menstrual irritability by 12 per cent. Cramps, backaches, fatigue, and tension were most prevalent during the menstruum; weight gain, skin disorders, painful breasts, swelling, irritability, mood swings, and depression were more prevalent in the premenstruum. Parity, oral contraceptive use, age, employment, education, and income were negatively associated with selected PMS. Use of an IUD, having long menstrual cycles, long menstrual flow, or heavy menstrual flow, and being able to predict the next period were positively associated with selected PMS. Race had both positive and negative effects on PMS.