C-reactive protein (CRP) is an acute phase reactant that is a reliable marker of systemic inflammation and has been associated with increased morbidity and mortality following hematopoietic stem cell transplantation (HSCT) in adults. In this study, we evaluated whether early elevations of CRP were associated with various complications and nonrelapse mortality following HSCT in pediatric patients. Seventy pediatric patients had CRP levels drawn at regular time points during the first week following their transplants. Patients were followed for 100 days following transplant, and transplant-related complications were documented. Patients who subsequently developed severe infections had higher median CRP values than those without severe infections (median 8.03 mg/dL versus 1.64 mg/dL, P = .0008) as did those who suffered nonrelapse mortality compared with those who did not (12.6 mg/dL versus 2.44 mg/dL, P = .02). These findings suggest that elevated CRP values may be useful as a marker of individual pediatric patients with a higher risk for treatment-related morbidity and mortality.