OBJECTIVE There is limited research on afebrile bacteremia. We aimed to compare the risk factors and outcomes of patients with afebrile and febrile infections. METHODS This was a retrospective cohort study of bloodstream isolates from 994 adults admitted to the emergency department of a university hospital. Afebrile infections, defined as the absence of fever history or measured fever through the emergency department course, was compared with febrile infection. Frequencies and proportions of sources of infection, comorbidities, along with organ failure and mortality were presented. The major outcome measure was 30-day survival. chi-Square or Student's t test was used for univariate analysis, and Cox proportional hazard model was used for multivariate analysis. RESULTS We found that the risk factors and outcomes of febrile and afebrile bacteremia patients were very different. The afebrile patients were older, have higher Charlson comorbidity index, and had poorer outcomes than the febrile patients. We also found that oldest old age, nonhematologic malignancy, necrotizing fasciitis, spontaneous bacterial peritonitis, and pneumonia were each positive independent predictors of afebrile bacteremia, whereas Escherichia coli infection and liver abscess were independent negative predictors of afebrile bacteremia. Finally, the 30-day all-cause mortality was higher in the afebrile group than in the febrile group (45% versus 12%, log-rank P<0.001). CONCLUSIONS This series of patients with afebrile bacteremia confirmed the previously reported associations with old age and immunocompromised conditions. Clinicians should explore the possibility of occult severe infection, and initiate early hemodynamic support and empirical antimicrobial therapy for patients with the aforementioned risk factors.