Objective. To compare the sensitivity of 3 different criteria--von Reyn, Duke, and modified Duke--in diagnosing infective endocarditis (IE) in children. Study Design. Retrospective case study in a tertiary pediatric hospital. Methods and Results. Between 1985 and 2001, 41 episodes of IE were documented in 40 children (median: 7 years old; range: 1 week to 18 years). The diagnosis was based on echocardiographic and microbiologic or pathologic findings. The initial echocardiogram suggested IE in 95% of the cases. Main findings were vegetations in 36, perivalvular absence in 4, and/or new valcular leaks in 6 cases. In 31 (76%) of the 41 episodes, the causative organisms were identified directly by polymerase chain reaction or serology. Sensitivities of the von Reyn, Duke, and modified Duke criteria in diagnosing IE were 63%, 81%, and 88%, respectively. In 10 cases (22%), the diagnosis of IE was "rejected" by the von Reyn criteria but was "definite" by the modified Duke criteria: 2 of the 3 cases had 1 major and [greater than or equal to]3 minor symptoms, and 1 had Q fever. Five episodes (12%) were classified as "possible" IE by the modified Duke criteria: although major findings were present on echocardiography, no organisms was identified "definite" from "possible" IE. Conclusions. The modified Duke classification was more sensitive in diagnosing IE in children than the von Reyn and Duke criteria. Still, 12% failed to be classified as "definite" IE by the modified Duke criteria. This illustrates the importance of positive BCs as a major IE criterion while significant echocardiographic findings are less considered by the presently used criteria. Pediatrics 2003;112:e467--e471. URL: http://www.pediatrics. org/cgi/content/full/112/6/e467; endocarditis, pediatric, diagnosis, infection.