To examine characteristics of medical malpractice claims involving radiation oncologists closed during a 10-year period. Malpractice claims filed against radiation oncologists from 2003 to 2012 collected by a nationwide liability insurance trade association were analyzed. Outcomes included the nature of claims and indemnity payments, including associated presenting diagnoses, procedures, alleged medical errors, and injury severity. We compared the likelihood of a claim resulting in payment in relation to injury severity categories (death as referent) using binomial logistic regression. There were 362 closed claims involving radiation oncology, 102 (28%) of which were paid, resulting in $38 million in indemnity payments. The most common alleged errors included "improper performance" (38% of closed claims, 18% were paid; 29% [$11 million] of total indemnity), "errors in diagnosis" (25% of closed claims, 46% were paid; 44% [$17 million] of total indemnity), and "no medical misadventure" (14% of closed claims, 8% were paid; less than 1% [$148,000] of total indemnity). Another physician was named in 32% of claims, and consent issues/breach of contract were cited in 18%. Claims for injury resulting in death represented 39% of closed claims and 25% of total indemnity. "Improper performance" was the primary alleged error associated with injury resulting in death. Compared with claims involving death, major temporary injury (odds ratio [OR] 2.8, 95% confidence interval [CI] 1.29-5.85, P=.009), significant permanent injury (OR 3.1, 95% CI 1.48-6.46, P=.003), and major permanent injury (OR 5.5, 95% CI 1.89-16.15, P=.002) had a higher likelihood of a claim resulting in indemnity payment. Improper performance was the most common alleged malpractice error. Claims involving significant or major injury were more likely to be paid than those involving death. Insights into the nature of liability claims against radiation oncologists may help direct efforts to improve quality of care and minimize the risk of being sued.