1. The term "observation hip" refers to a form of hip disease affecting children and adolescents, the most significant features being the transient nature of the symptoms and the absence of a bony or cartilaginous lesion on radiographic examination.

2. With a view to determining the possible sequelae of the disorder, twenty-three patients aged between two and fifteen years at the onset of the condition were studied fifteen to thirty years later.

3. Varying degrees of coxa magna, osteoarthritis or simple broadening of the femoral neck in the "observed" hip joint were found in the radiographs of twelve of the twenty-three patients studied.

4. This analysis suggests that the " observation hip" syndrome is the result ofan inflammatory process ofthejoint due to varied etiology, whether from injury or infection. The developmental and degenerative changes which may occur are a consequence of hypervascularisation of the bone. Thus changes may develop without necessarily producing the epiphysial necrosis characteristic of the first stage of ischaemia in Legg-Calvé-Perthes' disease.

5. The persistence of this stage of hypervascularity, and therefore the possible outcome of the transient synovitis, may be conditioned by the age at onset of the pathological process, the severity of the condition, and the duration of the symptoms and signs.