Clinical assessment of equinus in children before and after operation was made over a twenty-year period (1958-1978), and three groups were defined. Forty-three muscles (Group I) had abnormal shortening without spasticity and the deformity progressed steadily despite immediate improvement after operation; this was considered to be the result of a lack of muscle growth during bone growth. Forty-one muscles (Group II) had both shortening and spasticity with an imbalance which might be unchanged after operation, or reversed or improved. Fourteen muscles (Group III) had spasticity only and progression was unpredictable and could not be defined. Improvement in gait was regularly observed in Group I in the early years after operation. In Groups II and III the results were variable. These results did not depend on surgical technique but on differences in pathophysiology.