A 72-year-old man, healthy, smoker, with long-standing cough, was referred to our hospital and his chest X-ray (CXR) revealed a cavity lesion in the right upper lobe. Direct sputum smears, but not culture in solid medium, were positive for acid-fast bacilli (AFB) without tuberculosis DNA. The preliminary diagnosis was of a non-tuberculosis infection that progressed slowly, and the CXR showed the condition to worsen daily. Four years later, a commercialized mycobacteria growth indicator tube system was used to culture the colonies of AFB successfully in liquid medium, and the species was identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry. The patient responded well to triple therapy with rifampicin, ethambutol, and clarithromycin, the sputum cultures remained negative and the roentgenogram showed minor improvement over the following 6 months.