The pathophysiology, malignant potential, and hormonal therapy for benign breast disease remain controversial. This report investigates the anatomic and endocrinologic correlates of luteal phase mastodynia patients, compared with asymptomatic control subjects. Objective sonographic evidence of fibrocystic disease (FCD) was found in one-half of both mastodynia and control groups. Endocrine abnormalities observed in the mastodynia group included (1) significantly lower luteal phase progesterone and (2) prolactin hyperresponsiveness to thyroid-releasing factor. The presence or absence of anatomic FCD was not correlated with endocrine abnormalities. These data suggest that (1) cyclic mastalgia may be the end result of a dyshormonal milieu resembling the inadequate luteal phase; (2) FCD may be hormonally independent; and (3) cyclic mastalgia and FCD are different, if often coexistent, factors in benign breast disease syndromes.