Breast pain (mastalgia) and macroscopic breast cysts present commonly. Mastalgia may be improved by dietary manipulation to reduce saturated fat or supplement essential fatty acid intake. Fatty acid profiles were measured in women with mastalgia and breast cysts, before and during treatment with evening primrose oil, a rich source of essential fatty acids. The fatty acid profiles of both groups of patients were abnormal, with increased proportions of saturated fatty acids and reduced proportions of essential fatty acids. Treatment with evening primrose oil improved the fatty acid profiles towards normal, but this was not necessarily associated with a clinical response.