This international longitudinal study examines trends and changes in dental hygiene. Information was collected from national dental hygienists' associations through a series of five surveys conducted between 1987 and 2006; sample sizes increased from thirteen to twenty-five countries. As dental hygiene has evolved, it has remained remarkably consistent globally, in particular its scope of clinical practice. Regarding historical development, predominant work setting, and professional organisation, the profession was more similar than dissimilar. Greater variation existed regarding the supply, education, regulation, workforce behaviour and remuneration of dental hygienists. Over the 19-year period, there was a marked increase in supply accompanied by improved dental hygienist-to-population and to-dentist ratios, continuing high workforce participation rates, shift to and increase in the number of baccalaureate-level education programmes, and increase in scope of practice and professional autonomy including, for many countries, a decline in mandatory work supervision and slight increase in independent practice. By 2006, the profiles reflected the vast majority of the world's population of dental hygienists. While the rate of change varied, its nature was consistent overall, resulting in a continuing homogeneity in the profession worldwide. Observed trends and persisting issues have implications for service accessibility and technical efficiency and should continue to be monitored.