The aim of this study was to analyze the characteristics of patients with diffuse connective tissue diseases (CTDs) complicated by pneumomediastinum and identify the risk factors associated with increased mortality in these patients. Twenty-eight patients with CTD-associated pneumomediastinum, who were admitted to our hospital from January 1997 to June 2012, were prospectively studied. Their demographic characteristics, time to death, and potential risk factors were assessed. Survival curves were depicted by the Kaplan-Meier method. Univariate and multivariate survival analyses were performed by Cox regression. Of the 28 patients, 21 had dermatomyositis; two, polymyositis; three, systemic lupus erythematosus; one, polyarteritis nodosa; and one, undifferentiated CTD. The mean follow-up period was 1,461 days (54-5,264). The cumulative estimated Kaplan-Meier survival rate was 68 % at 1 week, 50 % at 1 month, and 43 % at 1 year. According to univariate analysis, higher serum albumin level (HR 0.87, 95 % CI 0.78-0.98), "slow air leak" (defined as time to progression of dyspnea [newly acquired respiratory failure, mechanical ventilation required, or decrease in PaO2 >30 mmHg after pneumomediastinum]) >3 days (HR 0.07, 95 % CI 0.02-0.34), and early initiation of immunosuppressive agents (within 1 month of steroid therapy; HR 0.27, 95 % CI 0.09-0.81) were associated with better prognosis. Final regression analysis revealed that slow air leak was associated with a lower mortality risk. We found that slow air leak was independently associated with better prognosis. Furthermore, most patients (86 %) who survived for at least 1 month following the pneumomediastinum event subsequently survived beyond 1 year.