The accessory navicular is occasionally the source of pain and local tenderness over the instep. If conservative measures fail, surgical treatment may be required and the results of 62 operations to one or both feet in 47 patients are reported. Twenty-six patients were treated by the Kidner operation, in which the main insertion of the tibialis posterior is re-routed; in the remaining 21 the ossicle was merely excised. Excision was as effective as the Kidner technique, provided that the medial surface of the main navicular bone was contoured to prevent any residual prominence. Both procedures were successful in relieving symptoms in the majority of cases and failures resulted from errors in the selection of patients or in the surgical technique. Correction of any associated flat foot was secondary to growth and maturation of the foot rather than to the operation; hence the Kidner procedure does not confer any particular advantages over simple excision.