In cases of sexual assault, victims often present too late for the detection of ethanol in biological samples. An ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS-MS) method was developed and validated for the determination of ethyl glucuronide (EtG) and ethyl sulfate (EtS) in urine. Sample preparation prior to UPLC-MS-MS analysis was a simple sample dilution. The calibration ranges were 0.2-20 mg/L, and between-assay relative standard deviations were in the range of 0.7-7.0% at concentrations of 0.3, 3.0 and 7.0 mg/L. Urine samples were analyzed from 59 female patients presenting to the Sexual Assault Centre at St. Olav University Hospital in Trondheim, Norway between November 2010 and October 2011. EtG and EtS results were fully concordant, and positive in 45 of the 48 cases with self-reported alcohol intake. In contrast, ethanol was detectable in only 20 of these cases, corresponding to sensitivities of 94 and 42%, respectively. Of the patients reporting no alcohol intake, none had positive EtG/EtS findings. These data show that analysis of EtG and EtS greatly increases the detection window of alcohol ingestion in cases of sexual assault, and may shed additional light on the involvement of ethanol in such cases. The victims' self-reported intake of alcohol seems to be reliable in this study, according to the EtG/EtS findings.