Composite lymphoma is a rare circumstance in which 2 or more distinct types of lymphoma occur in a single anatomical location. Although composite lymphoma has been increasingly identified with the advent of molecular genetic techniques, this topic has only rarely been a specific focus of the medical scientific literature. In this review, we focus on mantle cell lymphoma occurring as a major pathologic component of composite lymphoma and emphasize the clinicopathologic features of these tumors and associated biologic implications. To date, 26 cases of composite lymphoma including a component of mantle cell lymphoma have been previously published. Issues of clonal relatedness between the individual lymphoma components and emerging biologic implications as well as potential diagnostic pitfalls are evaluated. © 2012 Elsevier Inc. All rights reserved.