Insulin-like growth factor-1 (IGF-1) levels were analyzed in 43 healthy, nulliparous women aged 19-25 years. Blood samples were drawn in a standardized way in follicular and luteal phases, for present users during cycle days 5-10 and 18-23, respectively. In each women, absolute levels and a difference in p-IGF-1 levels between the two menstrual cycle phases (delta IGF-1) were related to oral contraceptive (OC) use, height, weight, age, gonadotropin and serum sexual hormone binding globulin (s-SHBG) levels. In the follicular phase and cycle days 5-10, absolute values of p-IGF-1 did not significantly differ between present, former and never users of OCs, in contrast to a significant difference (p = 0.0013) in the luteal phase and cycle days 18-23 between present users and never users, after adjustment for age. delta IGF-1 was significantly negatively correlated to present OC use, compared with nonusers (p = 0.0002). delta IGF-1 did not significantly differ between former and never users. While height and weight were not significantly related to delta IGF-1, there was a significant negative correlation between age and delta IGF-1 (p = 0.05). Also, s-SHBG and p-IGF-1 were significantly negatively related in the luteal phase and cycle days 18-23 after adjustment for age (p = 0.006), although this relationship disappeared after adjustment for present OC use.