Congenital non-spherocytic haemolytic anaemias are a heterogeneous group of disorders caused by an ineffective normal-type enzyme or, more commonly, by a structurally abnormal and ineffective mutant enzyme. The first part of this paper deals with the laboratory diagnosis of these diseases, which is based on a three-step approach: demonstration of the haemolytic nature of the disease, demonstration that the cause of haemolysis is intracorpuscular and demonstration of the presence of an absolute or relative enzyme deficiency. Moreover, the possible causes of false negative results in standard enzyme assays are briefly commented. The second part focuses on the main clinical, laboratory and biochemical features of the most common enzyme deficiencies of both the Embden-Meyerhof pathway and purine and pyrimidine metabolism, with particular mention of the cases identified in Italy.