Objective: — to evaluate the efficacy of inosit donation (Inofert, «Humana Pharma International SpA», Nutrilinea S.r.L. for Italfarmaco SpA, Italy) for improvement of quality of oocytes in PCOS patients; to assess quality of embryos after inosit donation; secondary outcomes of IVF cycles after inosit donation in PCOS women. Design — observational comparative multicenter research. Material and methods. Inclusion criteria: age <45, embryo transfer (ET) at IVF cycle. Exclusion criteria: age ≥45, severe extragenital disease, genetic (X-linked) syndromes. The patients of 1st group (n=133) were administered inosit 1000 mg + folic acid 100 mkg (Inofert, «Humana Pharma International S.p.A.», Nutrilinea S.r.L. for Italfarmaco S.p.A., Italy), during preconception care. The 137 patients of 2nd group were not administered inosit before pregnancy. Criteria of efficacy: pregnancy rates per ET, «take home baby», miscarriage rates. Results. The number of mature oocytes was significant higher in 1st group (p<0.001). Pregnancy rates per ET (87.0% versus 87.4%), «take home baby» (79.6% versus 89.4%), miscarriage rates (14.3% versus 10.6%) did not differ significantly. Conclusion. Inosit donation (Inofert, «Humana Pharma International S.p.A.», Nutrilinea S.r.L. for Italfarmaco S.p.A.) in PCOS women as a step of preconception care is the effective means improving quality of oocytes and influences prognosis of the IVF cycle positively. After inosit donation high pregnancy rates per ET and high index of «take home baby» can be seen. That substantiates inosit donation in PCOS infertile women prior to IVF.