Collagen vascular diseases that demonstrate features of interstitial lung disease include systemic lupus erythematosus, rheumatoid arthritis, progressive systemic sclerosis, dermatomyositis and polymyositis, ankylosing spondylitis, Sjögren syndrome, and mixed connective tissue disease. At histopathologic analysis, interstitial lung diseases associated with collagen vascular diseases are diverse and include nonspecific interstitial pneumonia, usual interstitial pneumonia, bronchiolitis obliterans organizing pneumonia (BOOP), apical fibrosis, diffuse alveolar damage, and lymphocytic interstitial pneumonia. Although proportions of interstitial pneumonias vary, nonspecific interstitial pneumonia accounts for a large proportion, especially in progressive systemic sclerosis, dermatomyositis and polymyositis, and mixed connective tissue disease. The more favorable prognosis in interstitial pneumonia associated with collagen vascular diseases than in idiopathic interstitial pneumonias may be explained by the larger proportion of nonspecific interstitial pneumonia than of usual interstitial pneumonia. High-resolution computed tomography seems to help characterize and determine the extent of interstitial lung disease in collagen vascular diseases.