Following correction with the Ponseti method some idiopathic clubfeet still will relapse even after six years of age. A better understanding of the cause for these late relapses will greatly help in the management of this condition. We evaluated a consecutive case-series from 1948 through December 1984 including 209 patients (321 clubfeet). Patients were treated following the Ponseti method. Initial number of casts, age at relapse, neurological evaluation, and final treatment for the late-relapses were recorded. There were 12 patients (6%) having a relapse after the seventh birthday. In 4 of these patients (6 clubfeet) a neuromuscular disease was diagnosed, representing 33% of the late relapses. These patients were initially treated with an average of 4 casts (range: 2-6) with 2 requiring an Achilles tenotomy. Patients used the brace for an average of 4 years. The average age at the relapse prior to the suspicion of neuromuscular disease was 9 years (range: 8-11 years). Two patients had family history of neuromuscular disease (myotonic dystrophy and multiple core disease). In the other two cases (Charcot-Marie-Tooth Disease type IA and myasthenia gravis) neuromuscular disease was not suspected. All four patients required an anterior tibialis transfer, three had a plantar fasciotomy, and two had peroneus longus to brevis transfers. One patient required a subsequent posterior tibialis transfer and another patient a triple arthrodesis (myotonic dystrophy). In conclusion, late relapses in patients with idiopathic clubfoot may represent the onset of a previously undiagnosed neuromuscular disease, and should be thoroughly evaluated.