The aim of the study was to validate a translated version of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) in Hebrew speaking populations. The WOMAC was translated into Hebrew from its English version and its reliability and validity were studied. Before its use in patients, the Hebrew version was translated back into English by an independent translator and minor amendments were made to satisfy the original English versions designed by Bellamy et al. The Hebrew version of the WOMAC questionnaire was administered to 114 patients with osteoarthritis of the knee. All the subjects were asked about the presence and severity of pain during movement and handicap, using a visual analogue scale (VAS) of pain and handicap. Test-retest reliability was assessed using Pearson's and intraclass correlation coefficients. Internal consistency was evaluated by Cronbach's alpha coefficient of reliability. Construct validity was tested by correlating the WOMAC items with VAS of pain and handicap. The test-retest reliability Pearson's correlation coefficients for the WOMAC items ranged from 0.55 to 0.78 (p<0.01), and the Cronbach's alpha was 0.97 at time 1 and 0.98 at time 2. Significant correlations (p<0.01) were obtained between the WOMAC items and VAS of pain and handicap. The Hebrew version of WOMAC is a reliable and valid instrument for evaluating the severity of osteoarthritis of the knee in Israeli patients.