The accuracy of a simple, pneumatic, direct-recording spirometer suitable for office use was evaluated by comparing spirometry on a water-sealed, 13.5-liter, water-filled spirometer for 120 patients. Good correlation between the two spirometers was seen through a wide range of values for forced vital capacity, forced expiratory volume in one second, and forced expiratory flow during 25% to 75% of forced vital capacity, with coefficients of correlation being .988, .988, and .948, respectively. All correlations were significant. The pneumatic spirometer is accurate, simple to operate, and suitable for spirometry in the office and clinic.