Purpose: To determine the incidence of anesthesia-related complications in children undergoing radiotherapy and the associated risk factors.Methods And Materials: We retrospectively investigated the incidence and types of anesthesia-related complications and examined their association with age, weight, oncology diagnosis, type of anesthetic (propofol vs. propofol and adjuncts), total propofol dose, anesthetic duration, type of radiotherapy procedure (simulation vs. radiotherapy) and patient position (prone vs. supine).Results: Between July 2004 and June 2006, propofol was used in 3,833 procedures (3,611 radiotherapy sessions and 222 simulations) in 177 patients. Complications occurred during 49 anesthetic sessions (1.3%). On univariate analysis, four factors were significantly associated with the risk of complications: procedure duration (p