There is a need for long-term surveillance of health behaviors, such as physical activity, to plan health promotion programs and understand if these programs have been effective. In this case study, we outline a descriptive epidemiological study where we examined trends in physical activity in Australia over a 22-year period through secondary analysis of population-based data sets. We used national data collected by the Australian Bureau of Statistics at six time points from 1989–1990 to 2011–2012. The data we used consisted of questions about walking, and moderate and vigorous leisure-time physical activity. Although the questions asked in the surveys had changed slightly over the six measurement points, we were able to harmonize the relevant variables for comparison purposes. There were strict data access protocols in place to protect the confidentiality of survey data, including applying for data access by the research team and the logistics of working with data in the Australian Bureau of Statistics Data Laboratory. Given the richness of the data and general sampling of the respondents, these national data sets are well worth pursuing. When designing long-term surveys for monitoring population engagement in health-related behaviors, the consistency in wording of questions is key to assure that the survey results can be compared and that we can draw appropriate and meaningful conclusions.