The aim of the study was to investigate knee cartilage thickness in polycystic ovary syndrome (PCOS) patients using ultrasonography and to assess the effects of sex steroids on osteoarthritis development. A total of 90 female patients were enrolled in the study, including 47 patients diagnosed with PCOS as study group and 43 patients admitted to our hospital for any other complaints as control group. Ultrasonographic evaluation of both knees was performed in all patients. The knee cartilage thickness was measured at lateral condyle, intercondylar area and medial condyle. The measurements were averaged for each region. The mean femoral cartilage thickness was greater in the study group compared with control group in all regions, with a statistically significant difference (p<0.005). In conclusion, we found PCOS patients to have greater mean cartilage thickness, supporting the possible effects of sex steroids on osteoarthritis development.