Hemangioma of the knee is a cause of pain and recurrent hemarthroses in the pediatric age group, often seen as an internal derangement of the knee. Historically, long delays in diagnosis have occurred. Conventional radiographic techniques can miss the presence of the lesion. However, magnetic resonance imaging (MRI) is a noninvasive and frequently diagnostic investigative modality. Five cases of diffuse synovial hemangioma of the knee are presented. Diffuse lesions are difficult to excise arthroscopically, and open wide excision is recommended after MRI and arthroscopic assessment.