Higher prevalence of polycystic ovary syndrome (PCOS) in women with type 1 diabetes (T1DM) is linked to exogenous insulin, especially when diabetes is diagnosed before puberty.The study evaluates the impact of prepubertal onset of T1DM and insulin therapy on PCOS diagnosis and phenotypic characteristics in women with T1DM.We studied 83 women with T1DM (age - 26±5 years, BMI - 24±3 kg/m 2) - 36 with premenarchal onset of T1DM (17 with PCOS diagnosed - PCOS+PM, 19 without PCOS - noPCOS+PM) and 47 with postmenarchal onset of T1DM (24 with PCOS - PCOS-noPM and 23 without PCOS - noPCOS-noPM).Clinical examination, assessment of serum sex hormones, glycated haemoglobin (HbA1c) and ultrasonographic evaluation of the ovaries were performed in all women.Applying Rotterdam criteria, 49% of women with T1DM were diagnosed with PCOS. There were no differences in hormonal profile and ovarian parameters between PCOS+PM and PCOS-noPM. Women with T1DM+PM had higher insulin dose/24h and U/kg bw/24h than T1DM-noPM (p=0.014; p=0.001, respectively). Both PCOS+PM and noPCOS+PM groups had higher insulin dose U/kg bw/24h in comparison to PCOS-noPM (p=0.004; p=0.006, respectively). In multivariable logistic regression analysis, age of menarche (OR: 0.672; 95% CI: 0.465-0.971) and HbA1c (OR: 0.569; 95% CI: 0.383-0.846) were associated with the diagnosis of PCOS.There were no differences in the prevalence of PCOS between T1DM+PM and T1DM-noPM; however, earlier menarche might have an influence on PCOS diagnosis in women with T1DM.