The menstrual cycle has been reported to alter pain perception but the patterns differ among studies. It has been reported that estrogens may influence somatic sensory processes. The present aim was to investigate whether the perception of pain varies by phases of the menstrual cycle. 20 women with chronic low pain volunteered to participate and were asked to rate their pain each day during three successive menstrual cycles. The menstrual cycle was divided into four and five phases to be able to compare results. Analysis showed there were phase differences in pain ratings during the menstrual cycle. Regardless of whether the menstrual cycle was divided into four or five phases, women rated pain significantly higher in the menstrual and premenstrual phases than in the midmenstrual and ovulatory phases. This is consistent with other studies showing less pain sensitivity during phases of the menstrual cycle associated with high estrogen. Women with high pain frequency reported more frequently a passive coping style and catastrophizing thoughts.