Anaplastic large cell lymphoma (ALCL) expressing the CD30 antigen is an uncommon subtype of non-Hodgkin's lymphoma characterized by distinct morphological and clinical features. The recurrent chromosomal abnormality found in these tumours is a t(2;5)(p23;q35) which has been detected in a minority of these cases, predominantly with a T cell immunophenotype. We report here a CD30 positive null cell type ALCL case cytogenetically characterized by a new type of t(2;5) translocation with distinct breakpoints at 2q37 and 5q31. FISH with a panel of 5q specific DNA probes applied in this case allowed for a mapping of a 5q31 breakpoint region between the locus for IL-3 (proximally) and CI5-56 probe (distally). These results point to a localization of unknown gene(s) on the long arm of chromosome 5 that, in addition to the NPM gene at 5q35, may be involved in the pathogenesis of some CD30+ ALCL.