As a consequence of experimental dislocation of the hip in puppies three to five weeks old, the following changes were observed: (1) acetabular dysplasia as early as four weeks following dislocation; (2) progressive dysplasia to the point of an unrecognizable acetabulum at the time of maturity; (3) nornmal acetabular development following experimental dislocation and immediate relocation: (4) pronounced changes in the head and neck of the femur, manifested by varus deformity of the neck, flattening of the head, and some reduction in the angle of anteversion of the neck; and (5) no abnormalities in the head and neck in the dislocated hips in which the femora were relocated.