INTRODUCTION: A prolonged corrected QT (QTc) interval in pediatric patients is defined as >/=470 msec. Methadone can cause a prolonged QTc interval that can lead to ventricular arrhythmias. The risk of methadone-induced prolongation of the QTc interval in children and young adults is unknown. The purpose of the study was to determine the frequency of QTc prolongation among pediatric and young adult patients with cancer pain on methadone treatment. METHODS: We retrospectively reviewed data for all patients on methadone during the study period. Qualifying patient data were reviewed to determine whether these patients had an electrocardiogram (ECG) while on methadone. The QTc values for analysis were manually calculated using the standard formula described by Bazett. RESULTS: Twenty-five patients were identified that met eligibility criteria. The median QTc decreased from baseline after initiation of methadone. QTc prolongation occurred in four of 25 (16%) patients and only one patient had a QTc greater than 500 msec. This patient had 17 normal QTc intervals on methadone prior to the prolongation. After resolution of electrolyte abnormalities, six subsequent ECGs on methadone had a normal QTc interval. CONCLUSIONS: Prolongation of the QTc interval is infrequent. The only observed case was transient during multiple comorbid conditions. A prospective study is justified to better understand what role methadone plays as one of many risk factors for prolongation of the QTc interval in children and young adults.