ABSTRACT : BACKGROUND : Mantle cell lymphoma (MCL) is a rare variety of non-Hodgkin's lymphoma which originates from CD5+ B-cell population in the mantle zones of lymphoid follicles. Coexistence of such tumours in the axillary lymph nodes with invasive breast cancers without prior history of adjuvant chemotherapy or radiotherapy has not been previously reported in literature. CASE REPORT : We report a rare case of breast cancer co-existing with stage I mantle cell lymphoma of the ipsilateral axillary lymph node detected fortuitously by population screening. CONCLUSION : Though some studies have tried to prove breast carcinomas and lymphomas to share a common molecular or viral link, more research needs to be done to establish whether such a link truly exists.