A case of tuberculous psoas abscess complicated during antituberculosis therapy for miliary tuberculosis and successfully treated with surgery was reported. A 20-year-old man visited our hospital because of fever lasting for 3 months. Chest radiography showed miliary nodules in both lungs and transbronchial lung biopsy revealed granuloma. Magnetic resonance imaging of the head showed small lesions in the brain. Computed tomography of the abdomen showed an enlarged paraaortic lymph node and a nodule in the spleen. Needle biopsy of the lymph node revealed necrotic tissue. Mycobacterium tuberculosis was not isolated; however, miliary tuberculosis was highly suspected based on clinical and radiographic findings. Once antituberculosis therapy was initiated with isoniazid, rifampicin, streptomycin, and pyrazinamide, the fever subsided. In spite of improvement of general radiographic findings, a new abscess was found in the right psoas major muscle after 8 months of therapy by computed tomography. A sample of the abscess showed a positive smear, negative culture, and positive PCR test for M. tuberculosis. Although antituberculosis therapy continued for another 6 months, the abscess enlarged to 7 cm and new retroperitoneal lymph nodes also appeared. Surgical drainage and curettage of the abscess was performed. Intra- and post-operative specimens were negative for bacteria, fungi, and M. tuberculosis. The patient was treated with isoniazid, rifampicin, and ethambutol for one year postoperatively. The disease disappeared without any evidence of relapse for 2.5 years after surgery.