External evaluations by an international committee of the scientific risk assessment and decision-making processes of the Netherlands Competent Authority for the authorisation of plant protection products and biocides (Ctgb) were conducted in 2013 and 2018. Based on the experience drawn from them, a general guidance for such visitations is suggested. An international visitation committee examined the structure and management of the Authority, its human resources and staff policy, the scientific processes and output, the documentation and communication of its decisions and the mechanisms for keeping up to date with international scientific developments. Attention was paid to the degree of openness and transparency throughout the organisation and in particular when dealing with confidential information. From the experience gained it can be concluded that visitations not aiming at finding mistakes and omissions but instead focusing on recommendations and constructive suggestions will result in cooperation, mutual trust and acceptance of the recommendations made. A follow-up visitation after a few years can be effective in maintaining a traceable, high-level scientific output. In view of the strong drive towards the European Union-wide harmonisation of the regulatory practices of hazardous chemicals, a voluntary evaluation of regulatory authorities’ scientific performance is recommended as a means for organisational learning.