We report the case of 17-year-old male adolescent immunocompetent patient with an operated transposition of the great arteries after the Mustard technique admitted to our hospital because of a cough and hemoptysis. Two nodules and an area of ground glass appearance located in the lower lobe of the left lung were diagnosed by ultrafast computed tomography (UF-CT) after ruling out cardiovascular complications. The gastric aspirate revealed acid-fast bacilli despite a repeatedly negative tuberculin skin test identified as Mycobacterium gordonae by the Gen-Probe Rapid Diagnostic Test. After an initial standard antimycobacterial therapy with isoniazid, rifampin and pyrazinamide the therapy was changed to clarithromycin and after a treatment course of 14 days, the UF-CT revealed a normal scan of both lungs. The case described suggests that one has to consider M. gordonae as a rare cause of infection even in immunocompetent patients.