Eleven patients with angiocentric immunoproliferative lesion (AIL) of the skin were studied. Histologically, three patients were grouped into AIL grade II (AIL-II), whereas eight showed angiocentric lymphoma (AIL-III). All the patients' specimens exhibited lobular panniculitis. Infiltrating atypical lymphocytes in nine patients possessed electron-dense membrane bound granules in electron microscopy. Phenotypically, the lymphoid cells in the AIL-II patients were positive for CD3 epsilon; two of these showed a positive reaction to CD2, CD7, and CD8, but lacked natural killer-associated (NKa) antigens CD16, CD56, and CD57. In six AIL-III patients, lymphoma cells were positive for CD2 in all patients, CD56 in five, CD3 epsilon in four, CD7 in four, interleukin-2 beta receptor in four, a pore-forming protein in four, and CD30 in three patients. The remaining two AIL-III patients had B-cell lymphoma. By the Southern blot analysis, three patients with AIL-III showed a rearranged T-cell-receptor beta-gene or a deletion of its germline. The preceding results in nine of 11 patients suggest that abnormal or neoplastic large granular lymphocytes with the characteristics of T and NK cells have an important role in producing the angiocentric/angiodestructive features and lobular panniculitis. Clinically, all three patients with AIL-II and four with AIL-III showed liver dysfunction, cytopenia, and abnormal coagulopathy during the clinical course. Five patients with AIL-III died within 8 months. The histological grading of AIL, patients' age, and limited clinical stage of the disease seem to correlate with response to the treatment and prognosis.