The stromal myofibroblastic reaction and extracellular matrix in a series of 19 morphologically and clinically aggressive basal cell carcinomas (BCC) were examined by an immunohistochemical staining panel for myofibroblastic markers (vimentin, actin, and desmin), for basement membrane components (laminin and type IV collagen), and for fibronectin. Results were compared with a series of 19 nonaggressive BCC. The aggressive BCC showed discontinuous staining for laminin and type IV collagen, a marked myofibroblastic response, and increased stromal fibronectin. Conversely, the nonaggressive BCC showed a continuous basement membrane and a total lack of staining for fibronectin and myofibroblastic markers in all but three cases. This report suggests that a combined analysis of extracellular matrix components and myofibroblastic markers may be useful for evaluating the clinical behavior including the metastatic capability of aggressive BCC.