 Using magnetic resonance imaging MRI to measure knee articular cartilage volume, we have demonstrated that post menopausal hormone therapy used for at least five years is associated with retention of articular cartilage in the knee, indicating that oestrogen may protect against the development of osteoarthritis in post menopausal women. Furthermore, we have recently observed that free testosterone is associated with loss of tibial cartilage, after taking into account age, body mass index, baseline tibial cartilage volume, tibial plateau area and total bone mineral content in healthy men. Whether an excess of testosterone to oestrogen as a consequence of aromatase inhibition has an adverse effect on articular cartilage volume warrants further investigation. 