The collagen vascular diseases represent a heterogeneous group of multisystem disorders with a wide range of clinicopathologic features. Although these diseases represent distinct clinical entities, a great deal of overlap exists between them. For example, the diffuse interstitial fibrosis of SLE, RA, DM-PM, PSS, and MCTD are indistinguishable clinically, radiographically, and histologically. Conversely, the pulmonary manifestations of the various vasculitides all differ significantly from each other in their clinicopathologic presentation, as well as in their response to therapy. For diagnostic purposes, histologic evidence will usually be required for the pulmonary manifestations of the rheumatic diseases. Therapy must then be individualized for each of these entities, as the protocol and response are variable.