BACKGROUND Chronic diseases are a major cause of mortality. Low levels of physical activity and sedentary behaviour are major risk factors for chronic diseases. Activity trackers can support adults diagnosed with a chronic disease to lead a more active lifestyle. OBJECTIVE To conduct a systematic review exploring the reporting of reach, effectiveness, adoption, implementation, and maintenance in interventions that used activity trackers in clinical care to improve physical activity or reduce sedentary behaviour in adults diagnosed with chronic diseases. METHODS A search of 10 databases and grey literature was conducted. Inclusion criteria included adults diagnosed with a chronic disease and the use of an activity tracker within clinical care. A RE-AIM framework data extraction tool was used to identify the reporting of 28 RE-AIM indicators. RESULTS Initially 4,585 studies were identified and after screening 15 remained for analysis. The RE-AIM dimensions of adoption and maintenance were underreported (mean percentage of indicators reported 3% and 13%). The use of qualitative methods to understand dimensions was only reported in 3 studies, 2 in effectiveness (12%) and 1 in implementation (7%). CONCLUSIONS Further research is required in the use of activity trackers to support patients to lead a more active lifestyle. Such studies should consider utilising the RE-AIM framework at the planning stage with greater focus on the dimensions of adoption and maintenance and using qualitative methods to understand the main RE-AIM dimensions within their design.