Soft-tissue vascular lesions in children can be classified as either hemangiomas or vascular malformations. The distinction between the two has important prognostic and therapeutic implications. Over the past 8 years, we have evaluated 64 vascular lesions with the technetium-labeled red blood cell (Tc-RBC) scan. Twenty-eight lesions imaged as hemangiomas with intense focal uniform uptake. This diagnosis was confirmed in 27 lesions, or 96 percent. Thirty-six lesions imaged as vascular malformations with abnormal vessels or diffusely increased activity. This diagnosis was confirmed in 35 lesions, or 97 percent. Overall, the Tc-RBC scan was 97 percent accurate in distinguishing hemangiomas from vascular malformations. It is particularly useful when the clinical diagnosis of the lesion may not be evident. Not only can biopsy be avoided, but parents can be reassured at an earlier age and given accurate information regarding prognosis.