In seven of 12 cases of Ber-H2 (Ki-1) positive anaplastic large cell non-Hodgkin's lymphoma (Ki-1 ALCL) disease remained localised to skin, and in five there was extracutaneous spread. Four patients had histological evidence of pre-existing or coexisting mycosis fungoides, and three patients had a long standing history of eczema or ichthyosis. In two cases the presence of a T phenotype was shown in frozen sections, and in a further six cases a T phenotype was firmly established in paraffin wax sections. Four patients died less than one year after presentation (two with disseminated lymphoma; two from other causes); one died at five years with widespread lymphoma and the remaining seven cases were alive one to 14 1/2 years after presentation. Three of the four patients with associated mycosis fungoides had prolonged survival, contrary to the findings of previous reports which suggest secondary Ki-1 ALCL behaves aggressively. The recognition of these tumours is important because of their relatively good prognosis. The diagnosis can be readily substantiated immunohistochemically, using a simple panel of antibodies.