This study investigated the association between appropriate antibiotic use, defined by validated quality indicators (QIs), and length of hospital stay in 1252 patients with complicated urinary tract infections. A dose-response relationship between good QI performance and shorter duration of stay was found. Background.  To define appropriate antibiotic use for patients with a complicated urinary tract infection (UTI), we developed in a previous study a key set of 4 valid, guideline-based quality indicators (QIs). In the current study, we evaluated the association between appropriate antibiotic use for patients with a complicated UTI, as defined by these QIs, and length of hospital stay (LOS). Methods.  A retrospective, observational multicenter study included 1252 patients with a complicated UTI, hospitalized at internal medicine and urology departments of 19 university and nonuniversity Dutch hospitals. Data from the patients' medical charts were used to calculate QI performance scores. Multilevel mixed-model analyses were performed to relate LOS to QI performance (appropriate use or not). We controlled for the potential confounders sex, age, (urological) comorbidity, febrile UTI, and intensive care unit admission <24 hours. Results.  Prescribing therapy in accordance with local hospital guidelines was associated with a shorter LOS (7.3 days vs 8.7 days; P = .02), as was early intravenous-oral switching (4.8 days vs 9.1 days; P < .001). There was an inverse relationship between the proportion of appropriate use in a patient (QI sum score/number of applicable QIs) and LOS (9.3 days for lower tertile vs 7.2 days for upper tertile; overall P < .05). Conclusions.  Appropriate antibiotic use in patients with a complicated UTI seems to reduce length of hospital stay and therefore favors patient outcome and healthcare costs. In particular, adherence to the total set of QIs showed a significant dose-response relationship with a shorter LOS.