This case describes an unusual presentation of a young adult with very late recurrence of stage MS neuroblastoma over 20 years after initial diagnosis. Tumor histology at relapse demonstrated ganglioneuromatous foci within her undifferentiated tumor. In combination with evidence of altered catecholamine metabolism, it proposes a case for dedifferentiation of unresected ganglioneuromatous lesions as the etiology of her recurrence of disease. An additional, compelling component of the case is the overall positive treatment response of the patient with relapsed neuroblastoma despite the poor prognostic factors of late relapse and adult age.