Treatment with the Ponseti method corrects congenital idiopathic clubfeet in the majority of patients. However, some feet do not respond to the standard treatment protocol. We describe the characteristics and treatment results of these complex idiopathic clubfeet. We identified 50 patients (75 clubfeet) from 762 consecutive patients treated at five institutions. Clinically, complex clubfeet were defined as having rigid equinus, severe plantar flexion of all metatarsals, a deep crease above the heel, a transverse crease in the sole of the foot, and a short and hyperextended first toe. The Achilles' tendon was exceptionally tight and fibrotic up to the middle of the calf. Correction was achieved in all patients by modifying the Ponseti manipulation and casting technique. Correction required an average of five casts (range, 1-10 casts). Two patients (4%) not initially recognized as having complex clubfeet had a posterior release with tendo Achillis lengthening. There were seven relapses that responded to casting. Three patients had a second tenotomy. Modifying the treatment protocol for complex clubfeet successfully corrected the deformity without the need for extensive corrective surgery.