The combination of piperacillin with tazobactam (PIP/TAZ) extends the activity of piperacillin against gram-positive, gram-negative, and anaerobic bacteria. The broad-spectrum of this formulation, together with its low degree of organ toxicity observed in adults, makes PIP/TAZ a tempting choice for children with radio-/chemotherapy-induced neutropenia. However, the use of PIP/TAZ is not yet approved for children under 12 years of age. The tolerability of PIP/TAZ was assessed in 19 children and adolescents between 2 and 18 years of age who developed a fever during aplasia after high dose radio-/chemotherapy and autologous stem cell transplantation (HD-SCT) for primary multifocal or relapsed solid tumours. Treatment with PIP/TAZ was initiated on average 3 days after HD-SCT, and the treatment was continued for approximately 10 days. Both clinical observation and laboratory studies showed no relevant alterations that would have been attributable to PIP/TAZ treatment. These results indicate that PIP/TAZ appears to be well tolerated in children during the acute phase of HD-SCT.