In a retrospective study of results of treatment in 160 children (265 feet) who had metatarsus adductus prospectively defined by severity and flexibility, we found that in 147 patients treated with plaster casts or casts followed by derotation splints the only significant predictor of a good outcome was the age of the patient. Results were statistically significantly better when treatment was begun from ages 1 day to 8 months. No significant correlations with poor results were found using the severity and flexibility grading systems. Given the public attitude toward deformity, it seems wiser to treat in infancy those feet graded "moderate" or "severe." If treatment is not commenced until the child is old enough to preclude conservative treatment, extensive surgery will be necessary to correct a "severe" deformity.