Introduction and Hypothesis: The aims of the study were the translation, cultural adaptation, and validation of the Incontinence Severity Index (ISI) for a Russian population. Methods: Following a forward- and back-translation of the original English ISI questionnaire into Russian (ISI-R), the translated questionnaire was reviewed by a group of patients as well as an expert panel. Women with urinary incontinence over 18 who gave informed consent were recruited in a validation study. They completed ISI-R and International Consultation on Incontinence Questionnaire ICIQ-UI Short Form (ICIQ-UI SF), as well as a sociodemographic checklist, and performed the 1-h pad weight (pad) test to measure urine leakage using pre-weighed absorbent pads. The psychometric properties of ISI-R were assessed. Results: A total of 213 women with urinary incontinence were included in the study. Satisfactory content validity of the ISI-R was shown: content validity indices for comprehensibility were 0.90 for patients and 1.0 for clinicians. Acceptable internal consistency was observed: a Cronbach’s alpha value of 0.62 and an interclass correlation coefficient of 0.70. Spearman’s correlation coefficient was 0.42 between ISI-R score and pad test results, and 0.41 between four-level severity index and pad test results (p < 0.001). Strong significant positive correlation between the ISI-R score and the total ICIQ-UI SF score was obtained (0.82, p < 0.001). Moderate agreement between the pad test and the ISI-R was shown—quadratic weighted Kappa coefficient 0.425 (p < 0.01). Significant sensitivity to changes was demonstrated by assessing the changes in ISI-R scores before and 12 weeks after surgery. Conclusions: The ISI-R is an informative instrument to be used in clinical practice and research to assess and document the severity of stress urinary incontinence in women, particularly those undergoing surgery.