In order to group the pelvic obliquity into clinically useful classification and to develop appropriate guidelines for treatment, we evaluated 55 patients who had been treated between 1985 and 1993 for pelvic obliquity after poliomyelitis. Age at surgery ranged from 15 years to 49 years (average 27 years). Fixed pelvic obliquity after poliomyelitis was classified into two major types according to the level of the pelvis relative to the short limb and into four subtypes in each type according to the direction and severity of scoliosis. Forty-six patients had obliquity with the pelvis down (type I), and nine patients had the pelvis up (type II) on the short limb side. Subtype A: straight spine with localized lower lumbar compensatory angulation, mainly at the L4-5 intervertebral space. Subtype B: mild scoliosis with convexity to the short limb side, Subtype C: mild scoliosis with convexity opposite to the short limb side. Subtype D: moderate to severe paralytic scoliosis, which has a convexity to the short limb side in type I and opposite to the short limb side in type II. In the pelvis of type I-A, I-B and I-C deformities, abduction contracture of the hip was released on the side of affected short limb, and lumbodorsal fasciotomy was performed on the contralateral side of short limb, where iliolumbar angle converged and the pelvis was elevated, if necessary. In most cases, hip instability existed on the side of short limb and it was treated with triple innominate osteotomy, which also contributed to leg length equalization by lengthening. In type II-A, II-B and II-C deformities, it was necessary to perform a triple innominate osteotomy on the side of affected short limb with adducted unstable hip in most cases. Lumbodorsal fasciotomy was performed above the iliac crest of elevated hemi-pelvis with short limb, where iliolumbar angle converged. In case of abduction contracture of contralateral hip, contracted fascia was released. In the pelvis that had a type I-D or type II-D deformities, treatment might include bony surgeries such as spinal fusion or triple innominate osteotomy, with appropriate soft tissue release. We propose a systemic and comprehensive classification for fixed pelvic obliquity after poliomyelitis. According to this classification, we and decide to combine corrective surgeries, and find the side where the surgery should be performed.