Increases in the incidence of childhood acute lymphoblastic leukemia (ALL) have been reported in some countries, while other reports from similar geographical regions have indicated stable rates. The reasons for the discrepancies have been debated in the literature, with the focus on whether the observed increases are "real" or an artifact resulting from improvements in diagnosis, case ascertainment and population coverage over time. We used population-based data from Western Australia to investigate trends in the incidence of childhood ALL between 1960 and 2006. Age-standardized incidence rates (ASRs) and rate ratios (indicating annual percent change) were estimated using Poisson regression. Between 1960 and 2006, the ASR was 3.7 per 100,000 person-years, with an annual percent increase of 0.40% (95% CI: -0.20, 1.00). Between 1982 and 2006, the ASR was 3.8, with an annual percent increase of 0.80% (95% CI = -0.70 to 2.30). This increased to 1.42% (95% CI: -0.30, 3.0) when a sensitivity analysis was undertaken to assess the effect of excluding the final 2 years of data. Annual increases of 3.7% (95% CI: -0.50, 8.00) among children aged 5-14 years, and of 3.10% (95% CI: 0.50, 5.70) in girls, were observed for this latter period. These results were supported by national Australian incidence data available for 1982-2003. There may have been a small increase in the incidence of ALL since 1982 among girls and older children, but an overall increase appears unlikely. No impact of folate supplementation or fortification is apparent. (c) 2007 Wiley-Liss, Inc.