The purpose of this study was to develop a simple and sensitive CE-UV method to quantify erlotinib and metabolites in urine. Following liquid-liquid extraction, erlotinib, and metabolites were separated with a BGE whose composition was phosphate buffer (pH 2.5, 65 mM) with 0.5% Tween 20. The applied voltage was 22 kV, capillary temperature 25 degrees C and the sample injection was performed in the hydrodynamic mode. All the analyses were carried out in a fused silica capillary with an internal diameter of 75 m and a total length of 37 cm. The detection of target compounds was performed at 240 nm. The calibration was linear in the range 0.15-20 mg/L for erlotinib and metabolites. Inter-and intraday imprecision were less than 4%. This simple, sensitive, accurate, and cost-effective method can be used in routine clinical practice to monitor erlotinib concentrations in urine from nonsmall cell lung cancer patients.