The aim of this study was to determine whether dipstick urinalysis (DU) augmented the accuracy of clinical assessment in the diagnosis of urinary tract infection (UTI). The study was performed in 627 consecutive patients attending an adult emergency department (ED) in whom the clinical diagnosis of UTI was considered. We excluded 227 patients. Treating clinicians gave the probability of a UTI on an ordinal and continuous scale, before and after DU. The assigned clinical probabilities were then compared to the results of formal urine culture. The areas under receiver-operating characteristic curves (AUC) were calculated. We found that clinical assessment alone was effective in detecting those patients with a UTI from those without (AUC 0.75; p < 0.0001). There was, however, a statistically significant difference in the accuracy of diagnosing UTI after DU (AUC 0.87; p < 0.0001). Proportionately more patients with a moderate pre-test probability of UTI were re-assigned to a different probability rating following DU, compared to the low or high pre-test probability groups (p < 0.001). We conclude that DU in combination with clinical assessment is a superior method for diagnosing UTI than clinical assessment alone.