Background: T‐cell lymphomas make up approximately 10%–15% of lymphoid malignancies. The frequency of these lymphomas varies geographically, with the highest incidence in parts of Asia.Diagnosis: The diagnosis of aggressive peripheral T‐cell lymphoma (PTCL) is usually made using the World Health Organization classification. The ability of hematopathologists to reproducibly diagnosis aggressive PTCL is lower than that for aggressive B‐cell lymphomas, with a range of 72%–97% for the aggressive PTCLs.Risk Stratification: Patients with aggressive PTCL are staged using the Ann Arbor Classification. Although somewhat controversial, positron emission tomography scans seem to be useful as they are in aggressive B‐cell lymphomas. The most commonly used prognostic index is the International Prognostic Index. The specific subtype of aggressive PTCL is an important risk factor, with the best survival seen in anaplastic large‐cell lymphoma—particularly young patients with the anaplastic lymphoma kinase positive subtype.Risk‐Adapted Therapy: Anaplastic large‐cell lymphoma is the only subgroup to have a good response to a CHOP‐like regimen. Angioimmunoblastic T‐cell lymphoma has a prolonged disease‐free survival in only ∼20% of patients, but younger patients who have an autotransplant in remission seem to do better. PTCL‐not otherwise specified is not one disease. Anthracycline‐containing regimens have disappointing results, and a new approach is needed. Natural killer/T‐cell lymphoma localized to the nose and nasal sinuses seems to be best treated with radiotherapy‐containing regimens. Enteropathy‐associated PTCL and hepatosplenic PTCL are rare disorders with a generally poor response to therapy, although selected patients with enteropathy‐associated PTCL seem to benefit from intensive therapy. Am. J. Hematol. 90:666–673, 2015. © 2015 Wiley Periodicals, Inc.