A 65-year-old Japanese woman presented with disseminated erythematous patches, plaques, and nodules on the trunk and limbs. Histological examination showed diffuse and dense infiltrates located in the dermis and subcutis, composed of large pleomorphic T lymphocytes. Immunohistochemically, neoplastic cells were positive for blastic T-cell markers, but negative for CD30 (Ki-1) antigen. Based on the clinicopathological findings, a diagnosis of primary cutaneous large T-cell lymphoma was made. Despite systemic chemotherapy, the patient died 7 months after diagnosis. Gene expression profiling using complementary DNA microarrays indicated significantly increased expression of an apoptosis-inhibitory protein and certain cyokines and cytokine receptors (e.g. MCP-1, MCP-2, IP-10, and IL-2R gamma) in the tumour-indurated skin. Comprehensive gene expression patterning in additional cases may provide useful information regarding the biological and clinical behaviour of aggressive cutaneous lymphomas such as CD30-negative large T-cell lymphoma.