Participatory action research (PAR) advocates end-user involvement in various societal domains. This paper aims to identify and analyse impacts of PAR involving older persons as co-researchers, and how these impacts spread and are enhanced throughout the research process and after its completion. By impact we mean transformational change throughout and after a PAR study. We present a qualitative community-based research project involving older people who live in sparsely populated areas in the Netherlands, and explore three types of PAR impact: personal, interpersonal and community impacts. We demonstrate how these impacts unfold through expanding circles, from a personal to a community level, and how these circles enhance each other. The project was conducted by a PAR team consisting of one researcher and seven co-researchers. The data were collected from observations, interviews and minutes of meetings, which the team subsequently analysed. The results are presented as a narrative account, whereby four project stages are followed by reflection on the impact it made. The discussion addresses the circles of impact, and whether and how they can strengthen each other in community-based projects involving older people. The concluding remarks address the influence of group dynamics on PAR, whether frail older adults can be expected to take an active part in PAR projects and the extent to which the results from such community-based PAR projects can be generalised.