Objective: To perform a retrospective study comparing clinical and laboratory aspects of patients with acute rheumatic fever (ARF) and patients with post-streptococcal reactive arthritis (PSRA), to discern whether these are 2 separate entities or varying clinical manifestations of the same disease. Study design: We located the records of 68 patients with ARF and 159 patients with PSRA, whose diseases were diagnosed with standardized criteria and treated by 8 pediatric rheumatologists in 7 medical centers, using the Israeli internet-based pediatric rheumatology registry. The medical records of these patients were reviewed for demographic, clinical, and laboratory variables, and the data were compared and analyzed with univariate, multivariate, and discriminatory analysis. Results: Four variables were found to differ significantly between ARF and PSRA and serve also as predictors: sedimentation rate, C-reactive protein, duration of joint symptoms after starting anti-inflammatory treatment, and relapse of joint symptoms after cessation of treatment. A discriminative equation was derived that enabled us to correctly classify >80% of the patients. Conclusion: On the basis of simple clinical and laboratory variables, we were able to differentiate ARF from PSRA and correctly classify >80% of the patients. It appears that ARF and PSRA are distinct entities.