A personal radon monitor (PRM) has been developed and validated for use in studies of residential 222Rn exposure. A pilot study was performed in six New Jersey homes with elevated Rn concentrations. Occupants wore PRMs, and identical monitors were placed in many rooms of the home. Extensive assessment of PRM performance has been done. A simple model for personal Rn exposure has been tested and measured occupant exposures have been compared with stationary Rn measurements. The PRM works well, with precision limited by the counting error in the exposure range examined (2-100 kBq m-3 h). The PRM sensitivity is 2.2 kBq m-3 h, and its efficiency is 2.6 tracks (kBq m-3 h)-1 per 81 mm2 film.