A 68-year old woman with a long smoking history underwent lung cancer screening by low-dose computed tomography. This detected a 3.0 cm spiculated mass in the left upper lobe. Transbronchial biopsy revealed necrotizing granulomatous inflammation and cultures grew Mycobacterium kansasii. Given lack of symptoms and concerns over drug toxicity, the patient declined antimicrobial therapy and she was monitored radiographically. Serial CT scans at six and twenty-two months showed progressive resolution of the mass. We present the first report of Mycobacterium kansasii presenting as a solitary lung nodule that spontaneously resolved without treatment.