After ingestion of 2000 mg tiaprofenic acid (Surgam), a 14-year-old girl was admitted to the clinic. The ingested dose was tolerated without signs of systemic intoxication. Tiaprofenic acid, its metabolites, and products of chemical decomposition were identified by gas chromatography/mass spectrometry in the urine sample of the patient. Additionally, a previously unknown decomposition product of a metabolite was detected. For quantitation of the drug in plasma, a rapid and sensitive high-performance liquid chromatography assay was established.