To investigate possible causes of menstrual disorders and androgen-related traits in young women with T1DM. Fifty-three women with T1DM (duration 8.0±5.6 years), 41 women with PCOS and 51 controls matched for age (19.4±4.3 vs. 21.2±2.7 vs. 20.8±3.1 years, p>0.05) and BMI (22.2±2.7 vs. 21.9±2.0 vs. 21.4±1.9 kg/m2, p>0.05) were prospectively recruited. Two women (3.8%) in the T1DM group had not experienced menarche (at 15.5 and 16.6 years); of the rest, 23.5% had oligomenorrhea, 32.1% hirsutism, 45.3% acne. The age at menarche was delayed in the T1DM group compared to controls (12.7±1.3 vs. 12.0±1.0 years, p=0.004), while no difference was observed with the PCOS group (12.4±1.2 years). There were no differences in total testosterone (0.43±0.14 vs. 0.39±0.14 ng/ml, p>0.05), DHEA-S (269±112 vs. 238±106 μg/dl, p>0.05) or Δ4-androstenedione (2.4±1.3 vs. 1.9±0.5 ng/ml, p>0.05) concentrations between T1DM and controls. However, patients with T1DM had lower SHBG concentrations than controls (61±17 vs. 83±18.1 nmol/l, p=0.001), which were even lower in the PCOS group (39.5±12.9 nmol/, p=0.001 compared with T1DM). FAI (free androgen index) was higher in the PCOS group compared with both other groups (T1DM vs. PCOS vs. controls: 2.53±0.54 vs 7.88±1.21 vs. 1.6±0.68, p<0.001). FAI was higher in patients with T1DM compared to controls, too (p=0.038). There was no difference in DHEA-S concentrations between T1DM and PCOS patients (269±112 vs. 297±100 μg/dl, p>0.05). Menstrual disorders and androgen-related traits in young women with T1DM may be attributed to an increase in androgen bioavailability due to decreased SHBG concentrations.