Haematuria, which was known at the time of Hippocrates, is defined as the presence of an anomalous number of red globules in the urine. It may present itself in a macroscopic or microscopic form. The latter is frequently found and is present in 1-2% of children. The pathogenesis of haematuria has been the object of recent acquisitions. The diagnosis is based in the first instance on the association of a positive urinary stick and confirmation of the presence of red globules in an assay of the sediment. The study of erythrocytic morphology is still the most useful test to identify the site of bleeding, even if more recently other markers, such as an excessive presence of acanthocytes or reduced mean corpuscle volume, together with the traditional study of cylindruria may represent elements to differentiate between glomerular and non-glomerular haematuria. Both family and personal medical history as well as objective examination play an important role in the definition of haematuria. Abdominal ultrasonography and biohumoral tests may, in association with the earlier data, allow a rapid and correct diagnosis of children with haematuria. A more detailed diagnosis using biopsy should be taken into consideration in selected cases, for example in familial forms that are not clearly defined and forms associated with altered renal function tests, as well as in persistent microhaematuria lasting for more than one year.