The local/regional incidence of off-label prescriptions can be difficult to estimate. Capture-recapture models can be used to indirectly estimate population sizes. Here, we used a capture-recapture model to estimate the number of patients treated off-label with baclofen for alcohol use disorder in northern France in 2013. Three capture sources were used: (i) the active case file at the region's largest Addiction Unit, (ii) the regional pharmacovigilance centre, and (iii) a sample of community pharmacies. After between-source overlaps had been identified, we used a log-linear model to produced eight estimates. Two models displayed the best goodness-of-fit, with estimates [95% confidence interval] of 1123 [714–2162] and 2180 [1598–2870] subjects, respectively. These two values are in line with a previous estimate of 1624 patients, based on an analysis of the French national health insurance database in 2013. Capture-recapture methods can be usefully applied to estimate the prevalence of OLPs in a specific geographical area, when direct counting is not feasible or the estimate through claim database is not possible.