Coxa vara can be a progressive deformity in children with skeletal dysplasia. Preoperative anteroposterior pelvic radiographs of 30 children with spondyloepiphyseal dysplasia congenita and spondyloepimetaphyseal dysplasia were used to test the reliability of a new radiographic measure of coxa vara, the Hilgenreiner-trochanteric angle. An additional 10 patients (20 hips) with coxa vara deformities needing valgus-producing proximal femoral osteotomies also were reviewed. Interobserver reliability with plain radiographs was 0.929 for the left side and 0.914 for the right side using interclass correlation coefficients. Intraobserver reliability also was high, with an interclass correlation coefficient of 0.875. Twelve hips corrected by osteotomy had adequate ossification to measure the Hilgenreiner-epiphyseal angle, head-shaft angle, and Hilgenreiner-trochanteric angle. Only one of these hips had a recurrence. The results were good in all of the other ossified hips. Eight hips had limited ossification; only two of these hips maintained acceptable alignment. Six hips had less postoperative correction and progressive deformity at the final followup. We present a novel measurement technique to determine the degree of coxa vara deformity in children with delayed or absent ossification of the capital femoral epiphysis.