Traumatic disruption of the acetabular triradiate physeal cartilage is an infrequent injury. When it occurs during adolescence, subsequent growth changes in acetabular morphology and congruency of the hip joint are unlikely. However, in younger children, especially those who are less than ten years old, acetabular growth abnormality is a frequent complication of this injury and may result in a shallow acetabulum similar to that seen in patients with congenital disease of the hip. By the time of skeletal maturity, disparate growth increases the incongruency of the hip joint and may lead to progressively more severe subluxation of the hip. Acetabular reconstruction may be necessary to correct the gradual subluxation of the femoral head. Variable irregularities of growth at the proximal end of the femur also may occur. In this series, nine patients with triradiate physeal-cartilage injury were classified according to the degree of displacement and the probable type of growth-plate disruption. Two main patterns of injury occurred. The first was a shearing type-1 or 2 growth-mechanism injury, with central displacement of the distal portion of the acetabulum. This injury pattern seems to have a favorable prognosis for continued normal acetabular growth, although premature closure of the triradiate physes may occur. The other pattern appeared to be a crushing type-5 growth-mechanism injury. This type has a poor prognosis, with premature closure of the triradiate physes occurring secondary to the formation of a medial osseous bridge. In either pattern, the prognosis is dependent on the age of the patient at the time of injury and on the extent of chondro-osseous disruption.