OBJECTIVES: To estimate the costs of unintended pregnancies (UP) over one year within the Russian health care system. METHODS: We calculated direct medical costs of a UP for women aged 15-44 per 5-year age groups (average per woman and per age group) as sum of the costs of pregnancy outcomes (live birth, termination, foetal loss, ectopic pregnancy) multiplied by the proportions of each pregnancy outcome that occurred following an UP. The costs of hospital and outpatient services for each outcome were calculated on the basis of information on typical practice provided in expert panel interviews, rates of pregnancy complications from federal statistics and reimbursement rates for medical services in obligatory medical insurance in Moscow region, adjusted for the proportion of medical expenditures covered by public budgets. The costs of live births were adjusted for mistimed pregnancies, based on literature data on their proportion for age groups. The numbers of UP were assessed using data from federal statistics on overall pregnancy outcomes and literature data on the proportion of these outcomes due to unintended pregnancies only. Based on the derived numbers we estimated the distribution of UP outcomes for each age group.  RESULTS: The average cost of UP per woman varied from 12 635 RUR (€309,68) for age group 15-19 to 17 630 RUR (€432,12) for age group 30-34. There are estimated to be annually 1 705 591 unintended pregnancies occurring in Russia, with direct medical cost amounting to approximately 26,4 billion RUR (€ 647,0 mln) annually. The highest costs are attributed to age groups 20-24 and 25-29, together accounting for 54% of overall cost burden of UP. CONCLUSIONS: The analysis has demonstrated that in Russia UPs elicit substantial health system costs, with the major part attributed to women aged 20-29.