Background Health care costs are rising. Identifying areas for health care utilization savings may reduce costs. Objective To identify oncology patients receiving inpatient radiotherapy with the purpose of measuring length of stay (LoS) and hospital charges. Methods During July 2013 the oncology service physicians at Mount Sinai Medical Center in New York City were surveyed daily to identify patients receiving inpatient radiation. Actual LoS, acuity LoS were determined from the chart review. Expected LoS was calculated using the University Healthsystem Consortium database. Charges associated with actual LoS, acuity LoS, and expected LoS were then reported. Actual and expected LoS were compared for inpatient radiotherapy and nonradiotherapy groups. Results 7 patients were identifed as having remained in the hospital to receive radiation treatment. In that cohort, the average actual LoS and charges per patient were 40.1 and $48,724, compared with acuity LoS and charges of 25.6 days and $34,089 and expected LoS and charges of 7.7 days and $10,028. Mean LoS and charges attributed to radiation alone amounted to 11 days and $12,514. The mean actual LoS of oncology patients admitted during the same time period who did not receive radiation was 6.7 days, compared with 40.1 days for patients who received radiation (P < .0001). Limitations Inability to access actual reimbursement data prevented exact cost calculations, small sample size, and single-institution focus. Conclusion Delivery of radiation therapy during inpatient hospitalization extends LoS and contributes to higher health care costs. Methods to facilitate the delivery of outpatient radiotherapy may result in cost savings.