Sacrococcygeal teratomas (SCT) are uncommon neonatal tumours which are usually benign. Our interest was aroused by encountering patients with reportedly benign SCT which later, after surgery, recurred as malignant tumours. We conducted a retrospective study of 17 patients treated for benign SCT during a period of 9 years. Of these patients, 4 developed malignant recurrence (3 females and 1 male) with a mean age of 19 months. The average time to recurrence was 17 months. Recurrence presented as a gluteal mass in one case, urinary and digestive compression signs in another case and as elevated alpha-fetoprotein levels in the two remaining cases. Histologically, one of the original tumors included tiny immature foci but none contained a malignant component after reading slides. Recurrences were as endodermal sinus tumour in all cases. After surgery and adjuvant chemotherapy, only one child died from complications related to chemotherapy. The other three were alive and well at mean follow-up of 5 years. These results emphasise the need for close clinical and biological follow-up for at least 2 years in all patients who had undergone excision of a neonatal SCT.