Japan pioneered and has maintained a nationwide mass screening programme for neuroblastoma since 1985 without prior evaluation among a target population. Convincing population-based evaluation of the ongoing programme has also been very limited because a population-based registry for childhood cancer has not been in operation. This report describes trends in incidence of and mortality from neuroblastoma in Osaka Prefecture, Japan, using Great Britain as an external control, between 1970 and 1994. Incidence and mortality rates were comparable between the 2 areas before the beginning of screening in Osaka. However, incidence rates were markedly increased in Osaka, especially among children younger than 1 year, from 25.9 per million children during 1970-1979 to 240.2 during 1991-1994, while age-standardized incidence rates for metastatic tumours among children aged 1 year or above did not decrease after introduction of the programme. Age-standardized mortality rates per million were unchanged at 3.9 (1970-1979) and 4.1 (1991-1994) in Osaka and 5.7 (1971-1979) and 5.0 (1991-1994) in Great Britain. Cumulative incidence rates among those up to 15 years old progressively increased from 103.4 per million (1970-1979) to 350.0 (1991-1994) in Osaka, though cumulative mortality rates did not decrease: 52.0 and 57.5, respectively. Corresponding figures in Great Britain were 101.0, 115.1, 78.6 and 70.1, respectively. The present findings show little beneficial effect of the screening programme.