Background: In-house guidelines are an essential tool of antibiotic stewardship (ABS) programs to guide antimicrobial therapy. We studied the effect of in-house guidelines adapted to the local pathogen and resistance epidemiology on prescribing behavior. Methods: At the University Hospital Halle (Saale) guidelines for the antimicrobial therapy and essential microbiological diagnostics were introduced. Main objectives were reducing the use of third generation cephalosporines and fluoroquinolones, decreasing selection pressure for enterococci and multidrug-resistant Gram-negative bacteria, minimizing Clostridium difficile infections (CDI), and improving microbiological diagnostics to enhance de-escalation strategies. 12 months thereafter a comparison of antibiotic consumption, pathogen and resistance statistics and use of blood cultures was performed. Results: There was a decrease of third-generation cephalosporines (-18.6%) and fluoroquinolones (-9.8%), while consumption of broad- and intermediate-spectrum penicillins (+23.8% and +37%) as well as carbapenems (+11.9%) increased. The total volume of prescribed anti-infectives remained unchanged. The number of enterococcal isolates (-18.3%) and CDI (-26.3%) decreased considerably. Gram-negatives, particulary ESBL-producing Enterobacteriaceae, were detected more frequently due to an expanded screening program. The rate of blood cultures/1000 patient-days was unaffected. Conclusion: In-house guidelines for the empiric antiinfective therapy appear to be suitable to influence the prescribing behavior and the selection pressure on individual pathogen groups. The total volume of antibiotic prescriptions was not affected in this study.