Knowledge about the deposition of airborne particles in the lungs is a key to understand effects of exposure to air pollution as well as estimating delivered dose from inhaled medicine. The majority of all research on deposition of inhaled particles in the respiratory tract has focused on healthy young adults. Nevertheless, it is typically other groups that are most affected, namely, patients with lung disease, elderly and children. These groups exhibit considerable differences in deposition of inhaled particles compared to healthy adults. This presentation will provide a summary of several experimental studies conducted over the past fifteen years, aimed at enhancing our understanding of aerosol deposition in vulnerable populations.