Background and purpose: Failure to recognize and to appropriately treat septic arthritis results in substantial morbidity rates. This study compared the demographic characteristics, risk factors, and outcomes of patients with community-onset septic arthritis due to Gram-positive and Gram-negative bacteria. Methods: The medical charts of 51 adults with culture-proven community-onset septic arthritis treated at a tertiary medical center in northern Taiwan from January 1, 2004 through December 31 , 2007 were retrospectively reviewed. The demographic data and clinical features were analyzed. Results: There were 39 patients with septic arthritis caused by Gram-positive cocci (76.4%) and 12 with septic arthritis caused by Gram-negative bacteria ( 23.6%). The most common pathogen was Staphylococcus aureus ( n = 30; 58.9%). The most frequently involved joint was the knee (n = 33; 63.5%). By multivariate logistic regression analysis, age (odds ratio [OR], 1.07; 95% confidence interval [ CI], 1.01-1.13; p = 0.024) and range of motion limitation (OR, 8.23; 95% Cl, 1.14-59.49; p = 0.037) were independent predictive factors for septic arthritis caused by Gram-positive cocci. Diabetes mellitus with end-organ damage (OR, 0.03; 95% Cl, 0.00-0.39; p = 0.007) and malignancy (OR, 0.04; 95% Cl, 0.00-0.66; p = 0.025) were negative predictive factors for septic arthritis caused by Gram-positive cocci. There were no significant differences in outcomes for patients with Gram-positive and Gram- negative septic arthritis. Conclusions: In adult patients with community-onset septic arthritis, older age and limited range of motion predict for Gram- positive cocci as the causative pathogen, while underlying diabetes mellitus with end-organ damage and malignancy predict for Gram-negative bacteria as the causative pathogen. ; 附設醫院內科部 ; 醫學院附設醫院 ; 期刊論文