The case of an 81-year-old ex-smoker male diagnosed with chronic bronchitis and undergoing treatment for pulmonary tuberculosis who presented a left iliac psoas abscess of torpid evolution is herewith reported. The detection of aerobic, anaerobic, fungal and mycobacterial microorganisms was repeatedly negative and was finally found to be an abscessed metastasis of epidermoid lung cancer. The aspects related to psoas abscess, muscular metastasis of bronchogenic carcinoma and the association between tuberculosis and lung cancer are discussed.