This study presents the time course of clinical and radiographic progression of symptomatic osteonecrosis of the femoral head and examines those characteristics which may be associated with more rapid progression. Clinical and radiographic progression occurred regardless of initial Ficat stage with some differences in the time course of progression. Radiographic progression was sensitive, but was less specific in predicting eventual clinical failure. Patients aged over 40 years with Ficat stage III hips progressed faster then did other patients with osteonecrosis. Hips with lesions occupying an area greater than 50% of the femoral head were uniformly associated with clinical failure. Clinical failure also correlated with the extent of collapse in Ficat stage III hips. In general, however, progression occurred relatively uniformly and suggested that symptomatic osteonecrosis of the femoral head is a progressive disease.