A pediatric intensivist in the University of Iowa Hospitals and Clinic's (UIHC) Pediatric Intensive Care Unit (PICU) was concerned about antimicrobial use in the unit. However, no one had quantified antimicrobial use in the UIHC's PICU or described the patterns of antimicrobial use in this unit. To address the intensivist's concern, the principal investigator (PI) conducted a retrospective study to determine the percentage of patients who received antimicrobial treatments, to determine the indications for antimicrobial use, and to identify antimicrobial agents used most frequently in the unit. On basis of our data, we hypothesized that empiric antimicrobial use, particularly the duration of therapy, could be decreased. We implemented a six-month intervention during which we asked the pediatric intensivists to complete an antimicrobial assessment form (AA) to document their rationale for starting antimicrobial treatments. We postulated that this documentation process might remind physicians to review antimicrobial therapies, especially empiric therapies, when the microbiologic data became available. In addition, we utilized the AA form to identify factors pediatric intensivists considered when deciding to prescribe empiric antimicrobial treatments. Data from the AA forms suggested that pediatric intensivists in the UIHC's PICU often considered elevated C-reactive protein, elevated white blood cell counts, and elevated temperatures when deciding to start empiric antimicrobial therapy. Data from the three nested periods showed that the median duration of empiric and targeted treatments decreased during the intervention and remained stable during the post-intervention period. The PI estimated that 193 days of empiric antimicrobial therapy and 59 days of targeted antimicrobial therapy, respectively, may have been saved by the decreased durations of therapy. Time series analysis assessing the trend in use of piperacillin-tazobactam, cefepime, and ceftriaxone (measured in mg/wk) did not reveal a significant change over time. On the basis of our results, an intervention strategy using an AA form alone may not be an effective strategy for antimicrobial stewardship in PICUs. Additional measures such as automatic stop orders and computer decision support may be useful for reducing the duration of empiric therapy in PICUs.