SUMMARY Over 7 years, 130 children were referred for prolonged isolated haematuria of unknown cause. In 34 instances, haematuria was also found in one or more family members. In 23 of these families (18 % of all referrals for isolated haematuria), investigation and follow-up, for periods of 5 to 10 years, of the index cases and of 56 haematuric relatives showed no evidence of renal disease and no other pathological findings. These subjects were diagnosed as having benign familial haematuria.The gene for benign familial haematuria is apparently transmitted as an autosomal dominant with reduced penetrance and variable expressivity. In Israel, the disorder seems to be more frequent among Jews of non-Ashkenazi descent than among those of European ancestry (Ashkenazim).Persistent or recurrent microscopical haematuria in otherwise healthy children represents a rather common clinical problem necessitating diagnostic procedures to identify or rule out renal disease, urinary tract pathology, or a haemorrhagic diathesis. Often, such examinations fail to reveal any cause for the haematuria. Many investigators (Baehr, 1926;Livaditis and Ericsson, 1962;Travis et al., 1962;Arneil et al., 1969;Johnston and Shuler, 1969;Glasgow et al., 1970) have concluded that the majority of such patients do not suffer from renal disease and have conferred upon them such diagnoses as 'idiopathic', 'benign', or 'essential' haematuria. In 1965, Ayoub and Vernier first reported a familial incidence of benign haematuria, a finding which has since been substantiated by others (McConville et al., 1966;Marks and Drummond, 1969;Rogers et al., 1973;Cotton et al., 1975). Since familial aggregation appeared to be a surprisingly common occurrence among children referred to our clinic because of persistent or recurrent haematuria, we decided to investigate all such cases seen over a 7-year period. Of these patients, 23 are believed to have benign familial haematuria (BFH). This paper describes the features on which the diagnosis was based and summarises clinical and genetic findings in this group of subjects.Received for publication 23 December 1978 Subjects and methods During the period 1966 to 1972, 130 children were seen in the Paediatric Nephrology Clinic of the Beilinson Medical Center with isolated, asymptomatic, persistent, or recurrent haematuria for which no cause could be found. This was defined as the finding of more than 10 erythrocytes per highpower field in 80 % or more of repeated urine examinations performed over a period of at least one year, and Addis counts showing more than 1 5 million erythrocytes per 12 h (our findings in healthy children are less than 0 5 million). In such cases urine analyses were performed on members of the immediate family (sibs and parents) and a family history was taken relating to renal disease, urinary findings, hypertension, deafness, and ocular anomalies. In 34 instances, haematuria was discovered in one or more members of the patient's family as a result of this search.The following investigations were ...