Background: High reach of target populations is relevant for public health impact of interventions. Concerning intervention programs requiring multiple contacts, little is known about how many persons may be kept in the intervention program over multiple time points. The aim of this study was to investigate (i) the reach of general hospital inpatients with at-risk alcohol use through screening and brief intervention and (ii) whether their continued intervention participation after hospital discharge differs by in-person vs. computer-based intervention (CO) delivery. Methods: As part of a randomized controlled trial, general hospital inpatients aged 18-64 years were screened for at-risk alcohol use on 13 wards. Participants were allocated to in-person intervention (PE), CO and assessment only. Both interventions were provided on site, and 1 and 3 months after baseline. Results: Ninety-two percent of all eligible inpatients (n = 6251) completed the screening. Eighty-one percent (n = 961) of the screening-positives participated in the trial and received their allocated intervention. At months 1 and 3, interventions were delivered to 83 and 79% of the CO participants and to 74 and 64% of the PE participants. The delivery of CO and PE required an average of 5.2 and 7.7 contact attempts per delivered intervention, respectively. Conclusion: General hospital inpatients with at-risk alcohol use were well reached through proactive interventions. COs may result in higher retention rates over 1 and 3 months and may require less contact attempts than PEs. Public health efforts that aim to achieve high intervention retention should consider proactive COs.