The excretion of an excessive amount of oxalates in the urine.

Oxalates consist of poisonous, colorless crystalline organic acid, found in many plants; such as, spinach, and made synthetically for bleaching, dyeing, rust remover, and cleaning.

High concentrations of oxalates may lead to formation of urinary calculi.

Hyperoxaluria may be genetic (primary), or secondary to ingestion or the administration of excess amounts of oxalate precursors, or to intestinal diseases.

Oxalates occur in plants and are toxic to higher animals by virtue of their calcium binding properties. They cause the precipitation of calcium oxalate in the kidneys, prevent calcium uptake in the gut, and are not metabolized.