Erdheim-Chester disease, adult periocular xanthogranuloma, juvenile xanthogranuloma, and necrobiotic xanthogranuloma are presumed to be separate disease entities, but they are often confused clinically because of their similar presentations and histopathology. To further describe the xanthogranulomatous diseases and to identify possible pitfalls in their diagnoses, we retrospectively reviewed charts from 1998 to 2001 for all patients with biopsy-proven xanthogranulomatous process of the eyelid and/or orbit. We found 2 patients diagnosed with adult periocular xanthogranuloma and 1 with Erdheim-Chester disease, each case initially misdiagnosed. Careful review of the clinical manifestations, histopathological review of all previous biopsy specimens, and repeat biopsy aided in the correct diagnosis and management of disease in these 3 patients.