A total of 41 non-cutaneous peripheral T-cell lymphomas were classified following the updated Kiel classification. Of these, 20 cases belonged to the low-grade group (T-cell chronic lymphocytic leukaemia, 3; lymphoepithelioid, 5; angioimmunoblastic, 4; pleomorphic small cell, 8) and 21 to the high grade group (pleomorphic medium and large cell, 11; immunoblastic, 3; large-cell anaplastic Ki-1 positive, 7). Seventy per cent showed a CD4+/CD8-phenotype, 39% a defective phenotype and 88% an activation phenotype. Eighty per cent had B-symptoms, 63% hepatomegaly, 48% splenomegaly and 26% had involvement of more than three lymphoid areas. Bone marrow was infiltrated in 34%, central nervous system in 4%, lung in 12% and skin in 14.6%. Seventeen per cent presented with extranodal disease and 82.8% had stage III/IV disease. Hypergammaglobulinaemia was found in 29%, hypercalcaemia in 7%, raised LDH serum levels in 58% and HTLV-I antibodies in only one case. Of the 37 treated patients 18 (48%) achieved a complete remission, but 33% relapsed. Mortality was 59% and actuarial overall survival at 38 months was 0.32. In the comparison of the clinical, analytical and immunophenotypic variables and outcome between low and high grade groups, only the average of bone marrow infiltration in the low grade and stage I-II, presence of defective phenotypes and higher Ki-67 positivity in the high grade group were significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)