The purpose of this investigation was to elucidate the impact of prompt intervention for patients whose blood culture results became positive during weekends, as this is not standard care in some countries. A retrospective cohort study was conducted in a tertiary referral hospital. From June 2015, results of positive blood cultures became available during weekends. If infectious disease specialists identified cases of bacteremia on suboptimal antimicrobial coverage, they contacted the primary team for modification of antibiotic treatment. We reviewed patients whose blood culture results became positive during weekends, comparing the pre-intervention (September 2014 to May 2015) and post-intervention (June 2015 to February 2016) periods. In total, 1081 (post-intervention 568 [52.5%]) bacteremia episodes were included (median patient age [interquartile range, IQR]: 72 [60-82] years; men: 625 [57.8%]). During the post-intervention period, 187 (32.9%) bacteremia episodes were detected during weekends. Infectious disease specialists evaluated the positive blood culture results 1, 2, and ≥3 days prior in 77 (13.6%), 88 (15.5%), and 22 (3.9%) cases, respectively. Although the 7- and 30-day mortality did not significantly improve after the intervention, the length of hospital stay (LOS) in the hospital-acquired bacteremia group was significantly reduced during the post-intervention period after controlling for confounders (post- vs. pre-intervention: median days [IQR]: 37 [19-63] vs. 46.5 [24.8-86.3], p = 0.030). Blood culture results became positive during weekends in one-third of bacteremia cases. The LOS was shortened after the intervention in the hospital-acquired bacteremia group. This could be an important antimicrobial stewardship target.