Objective: To compare metformin and combined oral contraceptive pill (COC) effects over 24 months in adolescent PCOS. Design: Randomized controlled study. Setting: Alexandria ICSI centre. Patients: 117 adolescent girls with PCOS, were randomized to: group A (n = 40): metformin, group B (n = 40): COC, and group C (n = 39): control. Interventions: Group A: received metformin, group B: received combined oral contraceptives. Main outcome measures: Improvement in cycle rhythm and hirsutism. Results: In group B a significant decline in serum testosterone reached the lowest value by the end of the second year (0.7 ± 0.2 versus 1.3 ± 0.5 lg/ml). By the end of the study, group A showed a significant decline in fasting (18.6 ± 3.0-10.0 ± 3.0 lIU/ml) and after-load insulin levels (126 ± 43-64 ± 15 lIU/ml) with a significant rise in glucose/insulin ratio (GIR) from 4.1 ± 0.3 to 4.6 ± 0.5. Group B showed a significant rise in fasting and after-load insulin (from 15.0 ± 3.0 lIU/ml and 103.0 ± 91.0 lIU/ml to 19.0 ± 4.0 and 187.0 ± 22.0 lIU/ml, respectively) and GIR dropped significantly from 4.4 ± 0.2 to 3.1 ± 0.3. Metformin was associated with a significant loss of weight from 87.0 ± 6.0 to 72.0 ± 0.5 kg while COC was associated with a non-significant gain in weight (from 84.0 ± 6.0 to 91.0 ± 9.0 kg). Conclusions: Metformin and COC have comparable therapeutic effectiveness on cycle regularity and hirsutism. Metformin was associated with a significant improvement in met-* Corresponding author at