This report presents a retrospective study of 34 Japanese children diagnosed at a single laboratory as having anaplastic large cell lymphoma (ALCL). Most of the pathological features of the Japanese ALCL children observed, such as anaplastic lymphoma kinase protein expression, in addition to most of the clinical characteristics and the outcomes of the patients, are very similar to those reported by European groups. To our knowledge, this is the first report describing the details of the clinicopathological features of Japanese ALCL patients. A further International study, including Japanese patients, might contribute to the establishment of an optimal treatment for paediatric ALCL.