Menstrual pain, dysmenorrhea, which is known to be prostaglandin mediated, can possibly be influenced by the dietary ratio of omega-3 and omega-6 polyunsaturated fatty acids. The prostaglandins derived from marine omega-3 fatty acids are normally less aggressive and therefore expected to be associated with milder menstrual symptoms. This hypothesis was surveyed in an epidemiological study in Danish women based upon self administered questionnaires concerning menstrual history, present symptoms, general health, socio-economic factors, and general dietary habits. Two prospective four-day dietary records were used to estimate average daily nutrient intake. The subjects were recruited by advertising, they were 20-45 years of age, not pregnant, and did not use oral contraceptives. No correlations were found between socioeconomic or anthropometric data and menstrual problems. However, certain dietary habits e.g. low intakes of animal and fish products, and low intakes of specific nutrients (omega-3 PUFA, B12 and omega-3/omega-6 ratio) were correlated with menstrual pain. The other nutrients in the diet were not significantly related to menstrual pain. The results were highly significant and mutually consistent and supported the hypothesis that a higher intake of marine, omega-3 fatty acids correlate with milder menstrual symptoms.