Hemangiomatosis of the skeletal system is a rare disease without specific symptoms and signs. We describe a 20-year-old patient with low back pain, whose plain radiographs of sacroiliac (SI) joint showed irregular sclerotic lesions. The patient was finally confirmed with skeletal hemangiomatosis by magnetic resonance imaging (MRI) and excisional biopsy of the lesion. The present case suggests that if patients with abnormal lesions of the SI joint in the plain radiographs do not have typical inflammatory back pain, advanced imaging is required to make an accurate diagnosis. Our case also emphasizes the importance of MRI and biopsy in establishing the diagnosis.