Intra-articular dislocation of the patella remains uncommon and is generally thought to be a problem of young adolescent males. This report reminds emergency physicians that it can occur in the arthritic knee, and it should be considered in the differential diagnosis of locked knee in the elderly. Closed reduction should be attempted in these cases, because the dislocation is liable to be held in place by osteophytes rather than impaction of the patella deep in the intercondylar notch and a good functional outcome can be expected.