Diffuse large B-cell lymphomas (DLBCL) constitute the largest subgroup of non-Hodgkin lymphomas (NHL) in adults. Although the etiology of NHL is not fully understood, different genetic abnormalities, involving particularly oncogenes, were shown as a mechanism of lymphomagenesis. Mutations of tumor suppressor genes, unlike oncogenes, have been relatively less studied in DLBCL. PTEN, a tumor suppressor gene located at 10q23, has been shown to be mutated or deleted in a variety of solid tumors. In this study, loss of PTEN expression was evaluated immunohistochemically in 102 patients with DLBCL. Partial or complete loss of PTEN was detected in about one-third of the cases, leading to the conclusion that it might contribute to the lymphomagenesis in some cases.