Objectives To determine in a prospective study whether urinary tract infection (UTI) in men younger than 45 years of age is associated with anomalies of the genitourinary tract that necessitate additional urologic evaluation. UTI in young men is uncommon. In these patients, it is customary to follow the same policy as that for children or older men and to routinely perform urologic investigations. Methods Twenty-nine consecutive, otherwise healthy, male patients aged 16 to 45 years (mean 30.5) were hospitalized for a first event of acute UTI. All patients underwent an imaging evaluation, including ultrasonography and intravenous urography. Those with macroscopic hematuria underwent cystoscopy. Uroflowmetry was performed at least 1 month after recovery, and patients with a maximal flow rate of less than 15 mL/s underwent a pressure flow study. Results Significant urethral stricture was excluded in all patients. Twenty-seven patients (93%) had a postvoid residual urine volume of less than 20 mL, and only two had values of 120 and 200 mL. The imaging and cystoscopic evaluation demonstrated a normal urinary tract in all patients. The maximal urinary flow rate was greater than 15 mL/s in 22 patients (76%) and lower than 15 mL/s in 7 patients (24%). In the latter group, urodynamic investigations, including free flowmetry and/or pressure flow study, revealed normal lower urinary tract function in 6 patients and a bladder outflow obstruction in 1 (3%). Conclusions A first event of UTI in men younger than 45 years is usually not associated with significant structural or functional urinary tract abnormalities. Therefore, no radiologic, endoscopic, or urodynamic investigation is required.