Objective To assess recruitment of children to national clinical trials for acute lymphoblastic leukaemia (ALL) and acute myeloid leukaemia (AML) in Great Britain during 1980–2007 and describe variation by some factors that might influence trial entry.

Design and setting Records of leukaemia patients aged 0–14 years at diagnosis were identified in the National Registry of Childhood Tumours and linked to birth registrations, Children's Cancer and Leukaemia Group records, Hospital Episode Statistics and Medical Research Council clinical trial registers. Trial entry rates were compared between categories of birth weight, congenital malformation, socioeconomic status and ethnicity.

Results 9147 ALL and 1466 AML patients were eligible for national clinical trials during 1980–2007. Overall recruitment rates were 81% and 60% respectively. For ALL, rates varied significantly with congenital malformation (Down syndrome 61%, other malformations 80%, none 82%; p<0.001) and ethnicity (South Asian 78%, other minority groups 80%, white 85%; p<0.001). For AML, rates varied with birth weight (< 2500 g 48%, 2500–4000 g 69%, >4000 g 67%; p=0.001) and congenital malformation (Down syndrome 28%, other malformations 56%, none 63%; p<0.001).

Conclusions Although recruitment rates to clinical trials for childhood leukaemia are high, future trials should monitor possible variation by birth weight, ethnicity and presence of congenital malformations.