In this prospective, controlled, randomized study, we compared the effect of a low-dose 21-day combined oral contraceptive (COC) containing 20 microg ethinyl estradiol (EE) and 75 microg gestodene (GTD) (Group A; n = 19) with an ultra-low-dose 24-day COC containing 15 microg EE and 60 microg GTD (Group B; n = 18) on bone turnover and bone mineral density (BMD) in young, fertile women. Nineteen healthy fertile women were used as untreated controls (Group C). At 3, 6, 9 and 12 months of the study serum osteocalcin (BGP), urinary pyridinoline (PYD) and deoxypyridinoline (D-PYD) were measured in all subjects. At baseline and after 12 months BMD was determined at lumbar spine by dual-energy X-ray absorptiometry in all patients. In both Groups A and B, urinary levels of PYD and D-PYD at 6, 9 and 12 months, were significantly reduced in comparison with basal values and with control subjects (p < 0.05). No significant differences in urinary PYD and D-PYD levels were observed between Groups A and B during the entire period of treatment. At 12 months, no statistically significant difference in spinal BMD values was detected between the three groups and in comparison with basal values. The present study suggests that the two COCs could exert a similar positive effect on bone turnover in young postadolescent women, without any significant and appreciable modification of BMD.