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Objectives To assess the representativeness of participants recruited through indirect methods into a cohort of healthcare professionals in the absence of comprehensive and up-to-date national registers.Design Comparisons of socio-demographic and socio-professional characteristics from multiple national data sources with those of a large indirectly recruited healthcare workforce cohort.Setting National healthcare workforce research conducted in Switzerland as a case study, with lessons applicable to other high-income countries lacking comprehensive registers.Participants Healthcare professionals across 10 professional groups, with data drawn from 14 administrative, institutional, professional and research sources collected between 2016 and 2023, alongside participants from the 2022–2023 baseline recruitment waves of the Swiss Cohort of Healthcare Professionals and Informal Caregivers (SCOHPICA).Main outcome measures Comparisons of age, sex, spoken language, training country, activity rate, working hours and sector of practice across available datasets.Results Broad similarities were observed in sex distribution between indirectly recruited participants and external data sources. However, discrepancies emerged in age profiles, linguistic distribution and certain profession-specific variables. These variations reflected both genuine diversity within the population and inconsistencies between available datasets.Conclusions SCOHPICA illustrates that in the absence of comprehensive and up-to-date registers, indirect participant recruitment can provide rich, diverse and generally comparable data on healthcare professionals, though representativeness cannot be definitively established. Such investigations offer valuable insights for monitoring and planning healthcare workforces internationally while underscoring the need for improved national registers and standardised workforce indicators.