Although many patients complaining of chest pain visit the emergency department, very few are diagnosed with spontaneous pneumomediastinum (SPM). We present the management of 20 patients with SPM.We retrospectively analyzed the clinical features, past history, chest X-rays (CXRs), 64-slice helical computed tomography (CT) images, and clinical course of 20 patients with SPM (19 men and 1 woman) who visited the emergency department of the Tokyo Metropolitan Bokutoh Hospital between 2005 and 2010.SPM predominantly resulted from physical exertion during such activities as sports and weight lifting (8 patients). The most common complaint was chest pain (15 patients), followed by dysphagia (10 patients), and dyspnea (8 patients). Subcutaneous emphysema was detected in 9 patients. The mean body mass index of the patients was 20.8±1.4kg/m2. Although CXR findings of pneumomediastinum were absent in 5 patients, CT showed findings of the Macklin effect in all patients—interstitial gas was observed in the perihilar area in all patients and in the peripheral lung area in 9 patients (45%). Ten patients were hospitalized. The others received ambulatory care in the form of analgesics without antibiotics. All patients fully recovered without complications.Our results showed that 64-slice helical CT is more reliable than CXRs for diagnosing SPM. Moreover, some patients with SPM can be treated without hospitalization, thus decreasing medical expenses for these patients.