Follicular lymphoma is a low-grade B-cell lymphoma of germinal center B-cell origin that typically lacks CD5 expression. We describe the clinicopathologic features of 88 cases of CD5+ follicular lymphoma (53 men, 35 women; median age, 60 years; range, 31-86). Follicular lymphoma was diagnosed initially in lymph nodes in 66 and extranodal sites in 22 patients. Eighty-one patients had lymphadenopathy, 66 had more than one involved site, 46 had bone marrow involvement, and 7 had splenomegaly. Staging information was available for 84 patients: 52 stage IV, 18 stage III, 12 stage II, and 2 stage I. Sixty-one cases were grade 1 or 2 and 27 were grade 3. The median proliferation index (Ki-67) was 30%. CD5 expression was detected by flow cytometry in 69, immunohistochemistry in 8, and both methods in 11 cases. The presence of t(14;18)(q32;q21)/IGH-BCL2 or other BCL2 translocation was detected in 28/44 (64%) cases. A total of 38 (43%) patients also had diffuse large B-cell lymphoma, concurrent with (n=20), subsequent to (n=13), or developing before CD5+ follicular lymphoma (n=5). All patients received chemotherapy; 12 also received stem-cell transplantation. With a median follow-up of 55 months (range, 0.5-207), 15 patients died, 46 were alive with disease, and 20 were in clinical remission. Compared with a matched group of patients with CD5- follicular lymphoma, patients with CD5+ follicular lymphoma more commonly had an International Prognostic Index >2 (35/80 vs 10/99, P<0.001), more often developed diffuse large B-cell lymphoma (38/88 vs 17/99; P<0.001), and had a shorter median progression-free survival (44 vs 89 months, P=0.0042). Higher Ki-67 and International Prognostic Index were identified as poor prognostic factors in both the groups. We conclude that CD5 expression in follicular lymphoma is associated with a higher International Prognostic Index, higher rate of transformation to diffuse large B-cell lymphoma, and shorter progression-free survival.