A total of 99 cases of viridans streptococcal endocarditis encountered during the period of 1973 and 1990 at the Veterans General Hospital-Taipei were reviewed to evaluate its prognostic factors. Applying strict clinical and laboratory criteria, 24 cases were categorized as definite, 44 probable, 23 possible and 8 likely. The symptoms were frequently subtle and atypical but initial laboratory tests gave useful indications: 69.1% with leukocytosis, 78% with anemia, 58.5% with elevation of LDH level, 88.9% with elevation of ESR value and 100% with elevation of CRP level. Furthermore, 32.4% of the cases demonstrated proteinuria and 67.4% microscopic hematuria. Seventy-three of the subjects had a history of underlying heart disease, predominantly rheumatic heart disease. Histological examination and echocardiography revealed that 51 patients suffered from vegetative endocarditis, 7 (13.7%) of whom were found to have anatomically confirmed vegetations without initial echocardiographic evidence, Vascular events were seen in 61 cases (61.6%): peripheral stigmata (32 cases), cerebral vascular accidents (17 cases), pulmonary embolism (10 cases) and others (2 cases). The overall mortality rate was 18.2%. Congestive heart failure with embolization was the most common cause of death in this group. The presence of vegetation was not well correlated with embolic events. There was no statistically significant association between the mortality and the following characteristics: age, sex, underlying heart disease, evidence of echocardiographically detected vegetations, major surgical intervention and recurrent cases except for embolic events (p less than 0.01). In conclusion, viridans streptococcal endocarditis complicated embolic events usually presented with a fulminant course and a grave outcome.