The randomized international trial for childhood anaplastic large cell lymphoma, (ALCL99-R1) involving European study groups and a Japanese group, compared six courses of methotrexate 1 g/m(2) over 24 hours with an intrathecal injection (IT) (MTX1 arm) with six courses of methotrexate 3 g/m(2) over 3 hours without IT (MTX3 arm). In this report, data from the Japanese portion of the trial are compared with the results of the international study. Overall, 352 patients were recruited for the international study, and 44 of these patients were from Japan. Median follow-up times were 3.8 and 3.5 years, respectively, in the international and Japanese studies. The two-year event-free and 2-year overall survival rates of the international study were 74% and 93%. The corresponding figures for those registered in Japan were 81% and 96%, respectively. Clinical characteristics and outcomes of patients were similar in the two groups. Incidences of grade 4 hematologic toxicity, infection, and grade 3 to 4 stomatitis, which were reported to be statistically significantly higher after the MTX1 arm in the international study, were also statistically significantly higher after the MTX1 arm for those registered in Japan. Results of ALCL99-R1 treatment in Japan were essentially the same as in the international study. The international study is anticipated to contribute to establishing an optimal treatment for ALCL, a rare childhood lymphoma.