We analyzed the clinicopathologic features of 13 patients with immunologically confirmed peripheral T-cell lymphoma. The lymphomas were classified into poorly differentiated lymphocytic, mixed cell, and large cell types. Marked morphologic heterogeneity was noted within the mixed cell and large cell categories, and the various subtypes are described. Twelve of the 13 patients received multiagent chemotherapy. Only three of the nine patients with poorly differentiated or mixed cell lymphomas achieved a complete remission, and the median survival for this group was 11 months. In contrast, all three of the treated patients with large cell lymphomas achieved a complete remission, two of whom are alive without disease (14 and 29 months, respectively). Classification of peripheral T-cell lymphomas into lymphocytic, mixed cell, and large cell types, as well as further subclassification within the heterogeneous groups, is suggested so that pathologic features of prognostic significance can be identified.