We report a 16-year-old previously healthy boy who presented with a 6-week history of fever, anorexia, weight loss, and respiratory distress. The chest radiograph showed bilateral upper infiltrates and cavitations indistinguishable from Mycobacterium tuberculosis infection. He was actually infected with M. kansasii. Treating Mycobacterium in an immunocompetent child requires multiple antimycobacterial drugs, including isoniazid, rifampicin, and ethambutol for at least 12 months after negative sputum culture.