A 73-year-old male presented a six-month history of buttock pain radiating into his thigh. The MRI revealed a large enhancing mass lesion involving the sacrum, with extension into the sacral canal. The tumor markers were measured to distinguish skeletal metastasis of carcinoma from primary bone tumor. The CA 19-9 was elevated. Despite the investigation, the primary site of cancer could not be found. Sacral bone biopsy was done. The pathologic examination revealed necrosis, chronic granulomatous inflammation, and multinucleated giant cells, consistent with tuberculosis. Sacral tuberculosis is rare in patients with no history of tuberculosis. Such solitary osteolytic lesions involving the subarticular region of large joints may mimic bone neoplasms and may be called "tuberculous pseudotumors." This case report intends to emphasize that bone tuberculosis should be a differential diagnosis in the presence of atypical clinical and radiological features. As tuberculous lesions may be mistaken for neoplasms, a small amount of fresh tissue should be sent for culture even if clinical diagnosis of a tumor seems likely. Described herein is a case of sacral tuberculosis mimicking metastatic bone tumor with elevated CA 19-9.