Despite an almost 80% overall survival rate in pediatric T-cell acute lymphoblastic leukemia (T-ALL), there is a subset of patients who are refractory to standard chemotherapy regimens and could benefit from novel treatment approaches. Over a 2-year period, we treated 5 pediatric patients with refractory T-ALL, aged 3 to 15 years, with high-dose cyclophosphamide (CY) at a dose of 2100 mg/m2 for 2 consecutive days either alone (n=1) or in combination with other chemotherapy agents (n=4). Four of these 5 patients had a 1.5 log decrease in disease burden. Three of the 5 patients had no evidence of minimal residual disease (MRD) after high-dose CY. One patient developed transient grade 4 transaminitis and 1 patient developed grade 3 typhlitis. All 5 patients ultimately proceeded to hematopoietic stem cell transplant when MRD levels were <0.01%. Pediatric T-ALL patients with persistent MRD after treatment with conventional chemotherapy may respond to CY at escalated dosing.