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Background: The aetiology of childhood leukaemia is largely unknown. Analyses of geographical differences may enhance aetiologic insights. The reunification of Germany in 1990 provides a unique opportunity to evaluate incidence patterns and time trends in two merging countries with substantial lifestyle, social and socioeconomic differences. With this study we provide an extensive assessment of 28-year incidence patterns and temporal trends after the German reunification., Methods: We identified all children diagnosed with a lymphoid leukaemia (LL) or acute myeloid leukaemia (AML) before the age of 15 years between 1991 and 2018 using the German Childhood Cancer Registry (N = 14,922), and evaluated the incidence pattern and temporal trends in former East Germany compared to West Germany by subtype, age at diagnosis and sex., Results: Incidence rates of LL were substantially lower (around 20 %) in Eastern Germany compared to Western Germany at the time of reunification. This was followed by a remarkable increase in Eastern Germany across both sexes and age groups until around 2000, when incidence rates reached the same levels as those in Western German federal states. Thereafter, incidence rates remained rather stable with some indications of a slightly decreasing tendency in both Eastern and Western Germany (estimated annual percentage changes (EAPC) 2005-2018: East Germany = -0.8 %; West Germany = -0.4 %), driven by the 0- to 4-year olds. Overall, AML incidence rates were stable over time in Western Germany, while EAPC for Eastern Germany indicated an increasing tendency (EAPC 1991-2018 = 1.3 %) driven by the older children, mostly during the early 2000s and in most recent years., Conclusion: The underlying mechanisms driving the childhood leukaemia rates remain inconclusive. Linkage studies including individual and clinical data would be valuable in evaluating the impact of a population's social, socioeconomic and lifestyle changes on the risk of childhood leukaemia and disease aetiology overall., (Copyright © 2021 Elsevier Ltd. All rights reserved.)