A 35-year-old man presented with a four-year history of right hip pain and disability exacerbated by physical activity and weightbearing. The patient denied any prior trauma. He did not have any fever, chill, night sweat or weight loss. Right hip radiographs showed an expansile and septated lesion affecting the right acetabulum. Pelvic CT confirmed the large and aggressively appearing acetabular lesion with diffuse trabecular destruction. The tumor had cortical bone expansion with multiples foci of osseous erosion and disruption (Figure 1A, Figure 1B, Figure 1C, arrows). The tumor measured 8 x 5 x 12 cm extending from the inferior ilium to the ischium without definite adjacent soft tissue invasion. MRI showed a large lesion of the left iliac bone involving the acetabulum and ischium (Fig. 2, arrows). The mass was isointense to muscles on T1-weighted images and hyperintense on T2-weighted sequences. Cortical breaches were detected at the medial aspect of the acetabulum and iliac bone. There was no hip joint mass or effusion. Since CT and MRI showed features of an aggressive tumor, bone scan was obtained for search of potential metastasis. The whole body technetium-99m MDP scintigraphy showed increased radiotracer uptake of the right acetabulum and right ischium (Fig. 3, arrows) but did not detect any additional osseous lesion. An initial CT-guided bone biopsy showed rare fragments of reactive woven bone, several irregular aggregates of spindle cells with round to oval shaped nuclei, bland-appearing chromatin patterns and no apparent mitotic figures. The spindle cells were in a fibromyxoid matrix with presence of scattered thin-walled blood vessels and rare giant cells. There was no histologic evidence of plasmacytoma or giant cell tumor. This CT-guided biopsy was not diagnostic but favored a low-grade neoplasm. A subsequent surgical open biopsy reached the diagnosis of iliac bone hemangioma. Due to the large size of the tumor, a conservative approach was observed. Close follow-up for two years showed continuously increasing pain requiring radiation therapy. Additional two-year posttherapeutic monitoring witnessed clinical improvement with stability of the iliac hemangioma on cross-sectional imaging.