The time to positivity (TTP) of blood cultures has been associated with increased mortality in bacteremia caused by several microorganisms. The aim of this study is to evaluate the relationship between TTP and prognosis, clinical presentation and extended spectrum B-lactamase (ESBL)-production in patients with Escherichia coli bacteremia. This is a retrospective observational study involving 226 adult patients with E. coli bacteremia. Data collected included underlying diseases, clinical presentation, prognosis factors, TTP, ESBL-production and outcome. Thirty-one (14%) patients had severe sepsis and 29 (13%) septic shock at presentation. Thirty-three (14%) strains were ESBL-producers. Thirty-nine (17%) patients died during admission and 17 (7.5%) within 48 hours. The median TTP was 8.3 hours (range, 0.42–76.5). It was significantly shorter in patients with septic shock (6.23 h, range 1.12–47.29 h vs. 8.51 h, range 0.42–76.50 h; p = 0.018). Rapid growth of E. coli, Pitt index >1.5, non-urinary source and Charlson score >2 were selected as independent risk factors of in-hospital mortality by the multivariate analysis. ESBL-production was not associated with modifications in TTP. Lower TTP is an independent risk factor for septic shock and poor outcome in episodes of E. coli bacteremia. The TTP in E. coli bacteremia is not significantly modified by ESBL-production.