External fixation was compared to crossed Steinman pins and plaster for fixation after osteotomy about the knee in children. A group of 26 patients treated by external fixation was compared to a control group of 26 patients fixed with crossed Steinman pins and casting. The groups were matched for age, height, and weight. Overall there was a 100% union rate. Preoperative deformity and postoperative correction were similar in the two groups. The time to union was significantly longer, and there were significantly more complications in the external fixator group. There were 16 complications (62%) in the external fixator group and five (19%) in the control group. Complications included pin tract infections, peroneal nerve palsy, and delayed union. External fixation provides certain advantages for fixation after osteotomies about the knee in children but is associated with a variety of complications.