The study evaluated the accuracy and clinical impact of rapid diagnostics (RD) with or without antibiotic decision support (ADS) for hospitalized patients with urinary tract infections. A two-centre prospective intervention was conducted with 230 patients divided into three groups: RD-only (n = 59), RD plus ADS (n = 56) and a control group (n = 115). Mean laboratory turnaround time for RD was 10 h and 50 min. Of 115 microorganisms, 108 were correctly identified. The error rate for rapid susceptibility determination was 0.85%. Total antibiotic consumption, measured in defined daily doses (DDD), was lower in the intervention groups compared to the control group (ADS: 10.3 DDD, p = 0.01; RD: 10.9 DDD, p = 0.06; control: 13.0 DDD). No significant differences were observed in the use of broad-spectrum antibiotics (p = 0.816). Adherence to antibiotic guidelines was significantly better in the ADS group compared to the control group (p = 0.015) (RD vs control; p = 0.261). The ADS group also received fewer doses of ineffective antibiotics (ADS: 1.8 doses, p = 0.012; RD: 2.4 doses, p = 0.195; control: 3.4 doses). Length of hospital and ICU stays or 30-day readmission rates did not differ across groups. No in-hospital mortality was observed in any group.