OBJECTIVE: To compare disease progression and mortality between idiopathic interstitial pneumonia (IIP) and interstitial lung disease (ILD) due to connective tissue diseases (CTD) including scleroderma, rheumatoid arthritis, systemic lupus, polymyositis, dermatomyositis, Sjögren's syndrome, and mixed CTD. METHODS: A case-control study of patients with CTD-ILD (n = 46) and IIP controls (n = 51), seen at the University of Michigan between July 1,1998 and June 30,1999 and followed until March 30, 2002, was conducted. Survival analysis and Cox regression were performed to estimate survival, accounting for demographic and clinical parameters, including pulmonary function tests and high resolution computed tomography (HRCT) diagnosis and scoring. RESULTS: Median followup time was 4.4 person-years. Five-year survival in the IIP group was 51.9% (95% confidence interval [95% CI] 30.8-69.4) versus 43.4% (95% CI 21.1-63.9) in the CTD-ILD group. There were no significant differences among HRCT diagnostic categories between IIP and CTD-ILD. A fibrotic score > or = 2 was associated with decreased survival among the entire group. Age at diagnosis and most recent forced vital capacity were significant predictors of mortality when adjusted for IIP versus CTD-ILD diagnosis, sex, and interstitial score. CONCLUSION: Contrary to expectation, CTD-ILD compared with IIP appears to be associated with a worse prognosis when adjusted for age. A higher fibrotic score is suggestive of decreased survival.