Hydrotherapy for OA of the hip has rarely been evaluated in controlled studies. Forty-seven patients with OA of the hip were followed for 18 weeks. Patients were randomly allocated either to a regimen of home exercises or to twice weekly hydrotherapy for 6 weeks in addition to home exercises. There was an improvement seen in both subjective and objective measures in both groups with treatment. There was no significant difference between the two groups. Response to treatment appeared independent of age, sex and radiological severity. We conclude that for most patients, a carefully graded and supervised regimen of home exercises is beneficial and there is little benefit in adding hydrotherapy to this regimen.