Exposure to airborne particulate matter is associated with a number of negative health effects ranging from respiratorydiseases to systemic effects and cancer. One important factor for understanding the health effects is the individual variationin the respiratory tract deposition of inhaled particles. In this study, we describe an experimental set-up for size-resolvedmeasurements of the lung deposited fraction of airborne particles, covering the diameter range from 15 to 5000 nm. Theset-up includes a system for generating a stable aerosol with a sufficiently broad size distribution. We used a scanningmobility particle sizer and an aerodynamic particle sizer to determine particle number and size. The set-up was used toinvestigate individual differences in the deposition fraction (DF) of particles in the respiratory tract for a group of 67subjects of both sexes aged 7–70 years. The measured DF was applied to two model aerosols, one representing an urbanenvironment and one a rural environment, and the particle deposition rates were derived (i.e., the deposited amount ofparticles per unit time). Furthermore, the deposition rates were normalized to lung surface area and body mass – two dosemeasures that are considered relevant for the health effects of airborne particles. In addition to validation of the set-up, weshow that there is a large individual variation in DF, with some subjects having a DF that is more than twice as high as thatof others. Although we observe differences in the DF between different subgroups, most individual variation wasexplained neither by age nor by gender. When normalizing the deposition rates to lung surface area or body mass, thedeposition rates of children become significantly higher than those of adults. Furthermore, the individual variability islarger for the lung surface area or body mass normalized deposition rates than for DF