This article provides an overview of the pathologic features of adult orbital xanthogranulomatous disease, a rare heterogeneous group of disorders that includes 4 clinical syndromes: adult-onset xanthogranuloma, necrobiotic xanthogranuloma, adult-onset asthma and periocular xanthogranuloma, and Erdheim-Chester disease. The diagnosis is made by biopsy of the lesion, demonstrating tissue infiltration by the hallmarks of xanthoma cells and Touton giant cells. The differential diagnosis is broad, including syndromes within the adult xanthogranulomatous disease category as well as other entities involving the eyelid and the orbital tissues. Because of its rarity and sometimes close similarity to other disease entities, it is often misdiagnosed initially. This article focuses on the morphology and immunohistochemical patterns in diagnosis of adult orbital xanthogranulomatous disease with emphasis on adult-onset asthma and periocular xanthogranuloma in particular, its clinical features and associated systemic manifestations in differential diagnosis, as well as the current management strategy.