Urinary oxalate is considered to play a crucial role in the formation of renal stones. In this respect hyperoxaluria constitutes a special problem, mainly because of the specific physicochemical properties of oxalate. The appropriate management of patients with this disorder must be based on a thorough understanding of the absorption, metabolism and excretion of oxalate. Different reasons for high oxalate excretion as well as analytical problems and our current therapeutic possibilities are covered in this review.