The significance of asymptomatic microhematuria in children is unknown. In 1976 Dodge et al. found a "surprising" high prevalence of proteinuria and haematuria in 12,000 healthy schoolchildren and, in the absence of knowledge of the natural history, this finding prompted them to postpone urinary mass screening. Nonetheless, the progressive course of most chronic renal disease in adulthood argues for investigation of microhematuria in children to uncover any sub-groups "at risk" of kidney diseases. The sensitivity of screening for microhematuria could be increased by a questionnaire on family medical history? We have investigated 1554 boys and 1484 girls aged 3-12 years, from the school population of a rural district near Rome. A self-administered questionnaire on renal disease and related symptoms in families was distributed to the parents. Urinalyses were done on all the children except for those with diseases or symptoms related to the urinary apparatus and girls who were menstruating. Haematuria was tested for by dipstick ("Combur 7"; Boehringer), children with microhematuria were retested 10 day and 1 year later. On the initial 3038 dipstick tests 175 (5.76%) were positive, and 52 children (1.71%) had haematuria in all three specimens. The questionnaires were used only if they had been filled in properly (1821/3038). Of the 1821 valid questionnaires 121 (6.64%) revealed a family history of hypertension, but the frequency of such a family history was significantly higher for the 128 children with haematuria (14.8%, p < 0.005) and the 52 with persistent haematuria (23.0%; p < 0.001).