Mucositis can be a serious complication of hematopoietic SCT (HSCT). A previous phase II trial in 32 children undergoing HSCT reported a beneficial effect of the homeopathic remedy Traumeel S. The Children's Oncology Group sought to replicate the results in a multi-institutional trial. The study was an international multi-center, double-blind, randomized trial comparing Traumeel with placebo in patients aged 3-25 years undergoing myeloablative HSCT. Traumeel/placebo was started on Day -1 as a five-time daily mouth rinse. Efficacy of the treatment was assessed using the modified Walsh scale for mucositis, scored daily from Day -1 to 20 days after HCST. The main outcome was the sum of Walsh scale scores (area-under-the-curve (AUC)) over this period. Other outcomes included narcotic use, days of total parenteral feeding, days of nasogastric feeding and adverse events. In 181 evaluable patients, there was no statistical difference in mucositis (AUC) in the Traumeel group (76.7) compared with placebo (67.3) (P=0.13). There was a trend towards less narcotic usage in the Traumeel patients. No statistically beneficial effect from Traumeel was demonstrated for mucositis. We could not confirm that Traumeel is an effective treatment for mucositis in children undergoing HSCT.