A longitudinal evaluation of bone mineral density (BMD) and metabolism was performed in premenopausal women. During the 2-year observation period, the menstrual pattern, plasma estradiol and FSH levels as well as the values of bone markers and BMD did not show any significant modification in a group of eumenorrhoic women (n = 37). Conversely, in age-matched oligomenorrhoic women (n = 37) a significant (P < 0.05) increase in the cycle length with a concomitant significant (P < 0.05) increase in circulating plasma FSH and parallel decrease of plasma estradiol levels (P < 0.05) was evident. In this group a significant (P < 0.05) increase in both urinary excretion of OH-P/Cr and plasma BGP levels paralleled a significant (P < 0.05) decrease in radial BMD. These data suggest that premenopausal impairment of ovarian function can lead to a bone loss in a significant proportion of women in which prevention should be considered before menopause.