Primary hyperoxaluria is a rare hereditary disease. Two types have been identified. Type 1 is due to the deficiency of the liver-specific peroxisomal enzyme alanine:glyoxylate aminotransferase/serine: pyruvate amino-transferase whereas, in type 2, the deficiency concerns the glyoxylate reductase/D-glycerate dehydrogenase, a cytosolic enzyme present in the leucocytes and hepatocytes. In the elapsed decade, important progress in molecular biology led to the introduction of new strategies in the diagnosis and treatment of type 1 primary hyperoxaluria. However, the greater rarity of type 2 has so far prevented similar development. The present review recalls the normal metabolism of oxalic acid, details its deviations and their clinical consequences, and describes the methods of diagnosis and treatment to be presently recommended in primary hyperoxaluria.