Venous malformations are the most common type of congenital vascular lesions resulting from abnormal embryonic development of vessels. Typical venous malformations are easily diagnosed by skin color changes, focal edema, or pain as they are mostly present in the skin and subcutaneous tissue. Venous malformations in the skeletal muscles, however, have the potential to be missed because their involved sites are invisible. We describe a 15-year-old patient with extensive intramuscular venous malformations in the lower extremity with special emphasis on diagnosis and treatment.