OBJECTIVE: To describe the incidence of acute renal insufficiency and identify potential risk factors associated with this adverse medical event. DESIGN: A cohort analytic study of patients with documentedor suspected bacterial pneumonia. SETTING: Nationwide survey of 74 acute care hospitals across the US. INCLUSION AND EXCLUSION CRITERIA: A total of 1822 adult patients with documented or suspected bacterial pneumonia who were receiving a cephalosporin, penicillin, or an aminoglycoside were enrolled. Patients were excluded if the duration of antimicrobial therapy was <3 days or if the pneumoniawas judged to be nonbacterial. DATA COLLECTION: Clinical pharmacists completed standardized data collection forms on all patients enrolled in the study. Information regarding patient demographics, concurrent illnesses and medications, antibiotic administration, representative laboratory data, and the occurrenceof any adverse clinical event was specifically captured. Information regardingthe development of acute renal insufficiency was targetedas an event to be captured. MAIN OUT COME MEASURES: Univariateand multivariate analyseswere performed to identify significant risk factors for acute renal insufficiency. A subset analysis was similar lyperformed to identify risk factors associated with aminoglycoside-related acute renal insufficiency. RESULTS: Of the patients enrolled in this study, 8.2 percent developed acute renal insufficiency. Risk factors for acute renal insufficiency included renal disease, aminoglycoside therapy, nosocomial pneumonia, elevated estimated creatinine clearance prior to study entry, cardiac arrest/shock, congestive heart failure, total duration of antibiotics >7 days, clindamycin therapy, liver disease, and first-generation cephalosporin usage. Risk factors for aminoglycoside-related acute renal insufficiency identified via multiple logistic regression included amphotericin B, congestive heart failure, aminoglycoside trough concentration >1.5 mg/L, and clindamycin therapy. CONCLUSIONS: The risk factors identified for acute renal insufficiency suggest that severity of illness strongly influences the development of renal insufficiency. Theoretically, the results of this study could serve as a framework for developing risk prevention programs within individual hospitals. Specific risk factors could be identified for a patient population and risk factors that could be modified could then be targeted for intervention. This type of information can also assist cliniciansin predictingthe probability of the adverseevent for a particular patient and subsequently minimizing this risk by initiating intense monitoring or modifying the drug regimen.