A sensitive and reliable high performance liquid chromatograph-fluorescence detection (HPLC-FLD) method for the determination of diethylstilbestrol (DES) in human urine is developed. DES was derivatized with 4-(4,5-diphenyl-1H-imidazol-2-yl)benzoyl chloride (DIB-Cl) under mild conditions and separated isocratically on a C18 column. The detection limits of DES at a signal-to-noise ratio (S/N) of 3 was 0.5 ng ml⁻¹, and the recoveries for the addition of different concentrations of DES to samples were in the range of 78.5–88.3% with RSD (n = 5) of less than 6.4%. The method was successfully applied to the determination of DES in human urine samples.