We report a case of a 57-year-old man who developed a fibrosclerosing lesion in the submandibular gland and idiopathic retroperitoneal fibrosis (IRF) involving the unilateral periureteral region within a year. Both lesions were resected surgically because of the suspicion of neoplasm. Pathologic examination revealed similar histologic and immunohistochemical features for both lesions, namely, fibrosclerosis with prominent hyalinizing collagen bundles and proliferation of myofibroblastic cells, and a non-neoplastic reactive nature. There was infiltration by lymphocytes with prominent lymph follicles, plasma cells and macrophages. The histologic and immunohistochemical findings suggest that the two lesions were of a similar pathogenesis, which was possibly mediated by macrophages. We think that the present case may be an unusual form of multifocal fibrosclerosis. Although sialolithiasis is thought to be a major pathogenic factor for chronic sclerosing sialadenitis of the submandibular gland, the present case suggests that certain cases might have an etiology similar to IRF.