Phenmetrazine is a central nervous system stimulant and is currently used as an anorectic agent. The drug is abused and reported to cause death from overdose. This study describes a liquid-liquid extraction protocol for phenmetrazine from urine using l-chlorobutane and subsequent derivatization using perfluorooctanoyl chloride for gas chromatography-mass spectrometric confirmation. Quantitation of urinary phenmetrazine can be easily achieved by using N-propylamphetamine as an internal standard. The article describes: cross reactivity of phenmetrazine with the EMIT assay for urinary amphetamines; chromatographic properties of derivatized phenmetrazine; mass spectral characteristics of perfluorooctanoyl derivative of phenmetrazine; precision linearity and detection limit; and application of the assay. Figures, table, references