Purpose: Streptococcal bloodstream infections (BSIs) are common, yet prognostic factors are poorly investigated. We aimed to investigate the mortality according to streptococcal species and seasonal variation. Methods: Patients with streptococcal BSIs from 2008 to 2017 in the Capital Region of Denmark were investigated, and data were crosslinked with nationwide registers for the identification of comorbidities. A multivariable logistic regression analysis was performed to assess mortality according to streptococcal species and season of infection. Results: Among 6095 patients with a streptococcal BSI (mean age 68.1 years), the 30-day mortality was 16.1% and the one-year mortality was 31.5%. With S. pneumoniae as a reference, S. vestibularis was associated with a higher adjusted mortality both within 30 days (odds ratio (OR) 2.89 [95% confidence interval (CI) 1.20–6.95]) and one year (OR 4.09 [95% CI 1.70–9.48]). One-year mortality was also higher in S. thermophilus, S. constellatus, S. parasanguinis, S. salivarius, S. anginosus, and S. mitis/oralis. However, S. mutans was associated with a lower one-year mortality OR 0.44 [95% CI 0.20–0.97], while S. gallolyticus was associated with both a lower 30-day (OR 0.42 [95% CI 0.26–0.67]) and one-year mortality (OR 0.66 [95% CI 0.48–0.93]). Furthermore, with infection in the summer as a reference, patients infected in the winter and autumn had a higher association with 30-day mortality. Conclusions: The mortality in patients with streptococcal BSI was associated with streptococcal species. Further, patients with streptococcal BSIs infected in the autumn and winter had a higher risk of death within 30 days, compared with patients infected in the summer.