['Osteoarthritis (OA) is increasingly prevalent in the years after menopause. Epidemiological data suggest that the use of oestrogen replacement therapy (ERT) may protect against knee OA.', 'To test the hypothesis that long term ERT (longer than five years) is associated with increased knee cartilage in postmenopausal women.', 'The study involved 81 women (42 current users (> or = five years) of ERT and 39 who had never used it). Articular cartilage volumes were determined by processing images acquired in the sagittal plane using a T1 weighted fat suppressed magnetic resonance sequence on an independent work station.', 'After bone size had been accounted for, ERT users had higher tibial cartilage volume than non-users. Total tibial cartilage volume was 7.7% (0.23 ml) greater in the group of ERT users (2.98 (0.47) ml; mean (SD)) than in the untreated group (2.75 (0.50) ml). The difference, after adjustment for the significant explanatory factors (years since menopause, body mass index, age at menopause, and smoking), between the ERT users and non-users increased from 0.23 ml to 0.30 ml (95% confidence interval 0.08 to 0.52, p=0.008). These differences persisted after exclusion of women with OA.'] Do users of oestrogen replacement therapy have more knee cartilage than non-users?