T-cell prolymphocytic leukemia (T-PLL) is characterized by a post-thymic immunophenotype, salient chromosome abnormalities, and an aggressive clinical course. However, cases in which these features are absent have been occasionally reported in Japan. Here, clinical and biological features of 13 T-PLL cases, diagnosed between 1992 and 2009 in the Tohoku region of Japan, were compared with three Western series. Median age was 64 (range 40-78) years old, and the male to female ratio (12:1) was higher than that of the Western series (P<0.04). Presented manifestations were similar to those of Western cases, but central nervous system involvement, which is rare in Western cases, was observed in 3 of 13 cases (23 %) (P<0.04). Immunophenotypic patterns were similar to those of Western cases, but HLA-DR was positive in 6 of 9 cases (67 %), which is distinct from Western cases (0-9 %) (P<0.002). By chromosome analyses, 14q11 abnormality and trisomy 8q, which are common among Western cases (70-80 %), were not observed in any cases (P<0.002). Morphologically, seven were classified as typical type, five as a small-cell variant, and one as a cerebriform variant. Seven cases experienced an aggressive course, whereas six experienced an indolent course over a median follow-up of 50 months. In contrast to Western cases, clinical courses were closely correlated with morphological types; 86 % of typical types were aggressive, whereas 83 % of small-cell types were indolent (P = 0.025). On the basis of these observations, together with previous Japanese cases in the literature, we propose that Japanese cases of T-PLL may constitute a variant.