Many policies promote patient and public involvement (PPI) in health research and healthcare provision. However, research points to uncertainties about its impact. The aim of the article was to compare what types of impact have been reported in reviews of PPI in health research and healthcare, respectively, and to map differences and similarities between the review studies. A review of reviews was undertaken with a search strategy based on the PCC mnemonic for scoping reviews. Four online databases were searched. Studies published in English between the years 2000-2020, using a review-based method and aiming to demonstrate impact of PPI were included, resulting in sixty-one articles. More reviews of PPI impact in healthcare than in health research were found, although the latter included a larger number of empirical studies. Systematic reviews, quality assessment and quantitative studies were less common in health research. Many original studies were from the United Kingdom. In health research, reported impacts most often related to research design and delivery, while in healthcare the most commonly reported impacts were individual health outcomes/clinical outcomes. However, there is still uncertainty about the strength of evidence for PPI, in particular when it comes to collective involvement in healthcare, that is in policymaking and service improvement initiatives at hospitals or the like.