We measured ultrafine particle concentrations in 56 Danish residences, estimated the daily integrated exposure of the occupants and apportioned this exposure to source events. The residential daily integrated particle number (PN) exposure in the homes was substantial and source events, especially candle burning, cooking, toasting and unknown activities, were responsible on average for ∼65% of the residential integrated exposure. Residents of another 60 homes were then asked to carry a backpack equipped with a GPS recorder and a portable monitor to measure real-time individual exposure over ~48 h. UFP exposure occurring in various microenvironments was estimated. The fractional contribution of each microenvironment to the daily integrated personal exposure corresponded to the fractions of the day the subjects spent in each microenvironment. The home environment accounted for 50% of the daily personal exposure, indoor environments other than home or vehicles contributed with ~40%, and being in transit or outdoors contributed 5% or less.