Patients with mixed connective tissue disease (MCTD) exhibit clinical features of systemic lupus erythematosus (SLE), progressive systemic sclerosis or scleroderma (PSS), and polymyositis-dermatomyositis (PM-DM). In their sera is an unusually high titer of a circulating antinuclear antibody with specificity for a nuclear ribonucleoprotein antigen. Pleuropulmonary manifestations are common in MCTD and the incidence varies from 20% to 85%. The pleuropulmonary complications include pleural effusion, intersitial pulmonary processes, pulmonary arterial hypertension (PAH), pulmonary vasculitis, pulmonary thromboembolic phenomena, aspiration pneumonia, and hypoventilatory failure. Pulmonary vascular pathology with progressive PAH and cor pulmonale is the most serious complication of MCTD. The pleuropulmonary manifestations in MCTD are similar to the respiratory problems well recorded in SLE, PSS, and PM-DM. Even though the pleuropulmonary complications are common in MCTD, they may remain clinically inapparent until fatal complications ensure.