Background The aim was to investigate the suitability of a municipal registry office for alcohol screening and brief intervention. We analyzed whether trial participation and retention differ by alcohol- and health-related, demographic and socio-economic participant characteristics. Methods Over 3 months, all 18- to 64-year-old visitors of a registry office were systematically screened. Persons with alcohol consumption in the past 12 months (N = 1646) were randomized to brief alcohol intervention (BAI) or assessment only. BAI was delivered by computer-generated individualized feedback letters at baseline, 3 and 6 months. Logistic and ordered logistic regression models were used to investigate whether the odds of trial participation and retention depended on participant characteristics. Models were rerun separately for low-risk and at-risk drinkers with Alcohol Use Disorder Identification Test-Consumption scores ≥4/≥5 for women/men indicating at-risk drinking. Results The trial participation rate was 67% with higher odds of participation in younger adults (P < 0.001). Retention rates at 3 and 6 months were 85% and 81%, respectively. Higher retention was associated with older age, higher level of school education and non-smoking (all p-values ≤0.05). Low-risk drinkers were more likely to participate in the trial (P < 0.01) and in post-baseline assessments (P < 0.05) than at-risk drinkers. Conclusion Our data suggest that registry offices could be a suitable setting to reach people from the general population for BAI. Especially the understudied group of low-risk drinkers was well reached through BAI and showed high adherence. BAI that addresses alcohol consumers beyond those at risk may be well accepted in proactively recruited people from the general population.