BACKGROUND: Systematic assessments of a country’s health information system (HIS) help identify strengths and weaknesses and may stimulate actions for improvement. They represent a capacity-building process for the country assessed as well as for the assessor. The joint action on HISs (InfAct) developed a peer-to-peer assessment methodology adapting an established WHO support tool. The aim of this study is to identify lessons learnt and the added value of the InfAct peer assessment for the assessors. *** METHODS: A qualitative evaluation of the peer HIS assessment was performed based on 12 semi-structured interviews: nine interviews were carried out with assessors from nine participating countries, and three with an observer (present during assessments). The interviews were carried out between May 2019 and January 2020. Interviews were analysed using qualitative content analysis. *** RESULTS: The interviews revealed the experiences of the assessors mainly occurred in five areas: assessors strengthened their understanding of what a population-based HIS is; they strengthened their understanding of how a HIS operates in different countries; they learnt how to carry out a HIS assessment; they strengthened their organization, communication, negotiation and reporting skills and they strengthened the networks in health information within and between countries. *** CONCLUSION: Since the assessors are key personnel in their respective national health systems, the impact of the assessment is not limited to the assessor alone but may extend to stakeholders in their country. The deployment of the InfAct HIS peer assessment, anchored in systematic HIS capacity building across European countries, is recommended.