Composite lymphoma with follicular lymphoma (FL) and mantle cell lymphoma (MCL) components is rare and can pose a substantial diagnostic challenge. We report two cases of composite lymphoma with FL and MCL components occurring in lymph nodes. Both cases showed near total effacement of the lymph node architecture by grade 1 FL (CD10+ and BCL2+) with accompanying in situ MCL component (CD5+ and cyclin D1+) surrounding neoplastic follicles. The diagnosis of composite FL and MCL was confirmed by detecting the t(14;18)(q32;q21) and t(11;14)(q13;q32) in the FL and MCL components, respectively. Immunoglobulin heavy chain fragment length analysis in both cases showed identical dominant monoclonal peaks in microdissected neoplastic lymphoid cells from FL and MCL components. These findings suggest a common clonal origin for the FL and MCL components in both cases.