Summary The clinical and laboratory findings are reviewed in 147 cases of hereditary bleeding disorders investigated in the years 1956 to 1963. There was an unexpectedly large number of hæmophiliacs (55) in the series, many of whom were very mildly affected. The importance of mild hæmophilia as a cause of unexpected surgical bleeding is noted. The findings in patients with von Willebrand's syndrome were very variable, and about a third had a formal bleeding time when first investigated. The difficulty in diagnosis and distinction from mild hæmophilia is discussed. Menorrhagia was found to be a very frequent presenting symptom in females with this condition. A family affected by hereditary thrombocytopenia is described. This was considered to be a variant of the von Willebrand syndrome. The Hicks‐Pitney test was evaluated and found to be reliable as a screening procedure in patients with less than 30% antihæmophilic globulin.