['This study examined the influence of the menstrual cycle on pain and emotion in women with fibromyalgia (FM) as compared with women with rheumatoid arthritis (RA) and to healthy controls.', 'One hundred and twenty-five premenopausal women (21-45 years old) participated in this study (57 with FM, 20 with RA, and 48 controls). Pain and emotion assessments were conducted during the follicular and the luteal phases of the menstrual cycle.', 'Women with FM experienced more pain, menstrual symptoms, and negative affect than did women with RA and the controls. All women reported less positive affect during the luteal phase, although this pattern was more pronounced in women with FM and RA than in controls.'] Does menstrual cycle influence on pain and emotion in women with fibromyalgia?