The histological, immunophenotypic and clinical features of 19 primary cutaneous anaplastic large cell lymphomas (cutaneous ALCL) were compared with those of 18 primary nodal anaplastic large cell lymphomas (nodal ALCL) of T-cell or null cell type. Although cutaneous ALCL and nodal ALCL had identical morphological features, differences in surface marker expression and clinical behaviour were found. Immunophenotypical differences concerned the expression of epithelial membrane antigen (82% of the nodal ALCL were positive v. none of the cutaneous ALCL) and the cutaneous lymphocyte antigen (HECA-452), a possible skin-homing receptor on cutaneous T-lymphocytes (most tumour cells in 44% of cutaneous ALCL cases were positive, whereas nodal ALCL showed expression of HECA-452 on only few tumour cells (< 25%) in 18% of cases tested). Loss of T-cell markers was more pronounced for nodal ALCL. Patients with cutaneous ALCL were generally older (median 61 years) than patients with nodal ALCL (median 24 years) and, in contrast to the latter group, did not show bimodal age distribution. Survival after 4 years, using lymphoma-related death as an end-point, differed significantly between cutaneous ALCL and nodal ALCL; 92% for cutaneous ALCL and 65% for nodal ALCL (P = 0.04). The better survival of cutaneous ALCL patients could not be ascribed to differences in age, stage or initial mode of treatment. These data indicate that differences in immunophenotype and clinical behaviour exist between morphologically identical primary cutaneous and primary node-based ALCL. They indicate that the primary site is an important prognostic factor in predicting the clinical outcome of ALCL.