dUrinary tract infections (UTIs) and sexually transmitted infections (STIs) are commonly diagnosed in emergency departments (EDs). Distinguishing between these syndromes can be challenging because of overlapping symptomatology and because both are associated with abnormalities on urinalysis (UA). We conducted a 2-month observational cohort study to determine the accuracy of clinical diagnoses of UTI and STI in adult women presenting with genitourinary (GU) symptoms or diagnosed with GU infections at an urban academic ED. For all urine specimens, UA, culture, and nucleic acid amplification testing for Neisseria gonorrhoeae, Chlamydia trachomatis, and Trichomonas vaginalis were performed. Of 264 women studied, providers diagnosed 175 (66%) with UTIs, 100 (57%) of whom were treated without performing a urine culture during routine care. Combining routine care and study-performed urine cultures, only 84 (48%) of these women had a positive urine culture. Sixty (23%) of the 264 women studied had one or more positive STI tests, 22 (37%) of whom did not receive treatment for an STI within 7 days of the ED visit. Fourteen (64%) of these 22 women were diagnosed with a UTI instead of an STI. Ninety-two percent of the women studied had an abnormal UA finding (greater-than-trace leukocyte esterase level, positive nitrite test result, or pyuria). The positive and negative predictive values of an abnormal UA finding were 41 and 76%, respectively. In this population, empirical therapy for UTI without urine culture testing and overdiagnosis of UTI were common and associated with unnecessary antibiotic exposure and missed STI diagnoses. Abnormal UA findings were common and not predictive of positive urine cultures. U rinary tract infections (UTIs) are diagnosed in over 1 million emergency department (ED) visits each year in the United States (1). Sexually transmitted infections (STIs) are also commonly diagnosed in the ED. The Centers for Disease Control and Prevention estimates that nearly 20 million new STIs occur annually, many of which go undiagnosed and unreported (2). Lower UTIs and many STIs have overlapping symptomatology, including the traditional UTI symptoms of dysuria, frequency, and urgency. In addition, abnormal urinalysis (UA) findings of positive leukocyte esterase and pyuria are common in both UTIs and STIs (3-6). Thus, distinguishing between these infections can be challenging.Previous studies in ED settings evaluating women diagnosed with UTIs have demonstrated that only about 50% will have a positive urine culture and 10 to 50% will have an STI (5, 7-10). These studies suggest that UTIs are overdiagnosed and STIs are underdiagnosed in the ED. However, previous studies in the ED setting have several limitations. First, some studies (5, 8) used a cutoff of Ն10 4 CFU/ml of a single uropathogen to define a positive urine culture, which may be inappropriately high for some organisms and populations (11, 12). Thus, the incidence of UTI may have been underestimated. Second, some studies may have underdiagnosed STIs b...