Ethylene glycol is a toxic alcohol which may induce significant toxicity when ingested accidentally or intentionally. The main clinical complications of EG poisoning include central nervous system depression, cardiorespiratory instability and renal failure, which may be lethal if improperly treated. Although the demonstration of high plasma levels of ethylene glycol confirms the intoxication, such measurements are generally not obtained in the acute setting and can be misleading due to the rapid metabolism of EG. This implies the need for alternative, indirect, diagnostic methods, which reflect the metabolic fate of EG. These include an early and transient osmolar gap, followed by an anion gap metabolic acidosis and hyperoxaluria. Another frequent finding is a lactate gap between various methods of lactate measurements. An appropriate knowledge of these laboratory findings is essential for the diagnosis of EG poisoning, and for the initiation of antidote therapy (fomepizole) and hemodialysis in selected cases. These features are illustrated by the presentation of a prototypical case of EG poisoning, in which an incomplete diagnostic workup on hospital admission resulted in an unnecessary laparotomy and a significant delay in the management of the intoxication.