Ethylene glycol is a common household substance responsible for a large number of ingestions in the U.S. each year. In 2001, nearly 5,000 ethylene glycol exposures were reported with more than 1,600 patients requiring medical treatment. There were 16 deaths attributed to ethylene glycol in 2001, second only to ethanol overdose for lethal ingestions. Diagnosis of ethylene glycol ingestion is relatively straight-forward when an individual with a history of exposure is found to have a high anion-gap metabolic acidosis and an elevated osmolar gap. Appropriate treatment can be immediately employed and the diagnosis confirmed by the finding of elevated ethylene glycol levels in the serum. In the absence of exposure history, the differential diagnosis of a high anion-gap metabolic acidosis and an elevated osmolar gap will also lead to consideration of ethylene glycol ingestion. This well-recognized presentation of ethylene glycol toxicity includes findings expected in individuals who present for care soon after their ingestion. A less well-known pattern may be seen in those for whom care is delayed. We present a patient with delayed presentation of ethylene glycol ingestion and review the physiology and biochemistry that underlies this different presentation. Unfortunately, without history or strong laboratory evidence, ethylene glycol ingestion may be easily overlooked in individuals with delayed presentation.