Among patients who visited our hip clinic, eighteen patients from ten families were diagnosed as mild or atypical cases of spondyloepiphyseal dysplasia or multiple epiphyseal dysplasia. Clinical and X-ray examinations of these patients showed common characteristic features as follows. 1. They usually had short stature but were not dwarfs. Their facial features and body proportions did not suggest hereditary bone dysplasia. 2. Although the disease might be transmitted in an autosomal dominant manner, its occurrence among these families was found to be sporadic. 3. Symptoms of the hip joint mainly resulted from limited range of motion, coxalgia being usually less than expected from X-ray findings. 4. Joints were always affected bilaterally although the degree might be different on each side. 5. In the majority of the cases, the spine, shoulder (in 7 cases), knee (in 6 cases), elbow (in 3 cases), ankle, and wrist joint (in 2 cases) were also affected. 6. Characteristic X-ray findings of the hip joints were as follows. a) Coxa vara, flattening or rectanglar deformity of the femoral head and shortening of the femoral neck. b) The trabecular pattern of the femoral head was irregular and subchondral cysts were often observed. c) Joint space was relatively better restored than expected from the deformity and subchondral bony changes of the femoral head. Spondyloepiphyseal dysplasia and multiple epiphyseal dysplasia are genetic disorders of the epiphyseal and apophyseal cartilage. The hip joint is loading greater mechanical force than any other joint. In both spondyloepiphyseal dysplasia and multiple epiphyseal dysplasia, the hip joint is always affected. As the hip joint is most vulnerable when there is some disorder of the epiphyseal cartilage, it is probably the only detectable abnormal joint. In relatively short period (1972-1978), the diagnosis of mild or atypical spondyloepiphyseal dysplasia was made in 18 patients in our hip clinic. This means that the mild or atypical cases of spondyloepiphyseal dysplasia is not so rare as expected. They might be misdiagnosed as aseptic necrosis, deformity of the femoral head due to Perthes disease or primary osteoarthrosis. An extreme care should be taken when we examine such patients.