Premenstrual syndrome afflicts millions of premenopausal women and has been described as one of the most common disorders in women. Research over the past few years suggests that a variety of nutrients may have an important role in the phase related mood and behavioral disturbances of the premenstrual syndrome. There is scientific evidence, at least for a few of these micronutrients, specifically calcium and vitamin D, supporting cyclic fluctuations during the menstrual cycle that may help explain some features of PMS. Ovarian hormones influence calcium, magnesium and vitamin D metabolism. Estrogen regulates calcium metabolism, intestinal calcium absorption and parathyroid gene expression and secretion, triggering fluctuations across the menstrual cycle. Alterations in calcium homeostasis (hypocalcemia and hypercalcemia) have long been associated with many affective disturbances. PMS shares many features of depression, anxiety and the dysphoric states. The similarity between the symptoms of PMS and hypocalcemia is remarkable. Clinical trials in women with PMS have found that calcium supplementation effectively alleviates the majority of mood and somatic symptoms. Evidence to date indicates that women with luteal phase symptomatology have an underlying calcium dysregulation with a secondary hyperparathyroidism and vitamin D deficiency. This strongly suggests that PMS represents the clinical manifestation of a calcium deficiency state that is unmasked following the rise of ovarian steroid hormone concentrations during the menstrual cycle.