Few studies have compared the difference in pulmonary function in normal subjects while sitting in an upright posture as compared to a slumped posture. The purpose of this study was to demonstrate differences in tidal volume (TV), breathing frequency (fb), and minute ventilation (VE) between these two sitting postures in a population of healthy adults. A sample-of-convenience of 30 adult subjects (17 females and 13 males) participated in the study. Standard spirometry methods were used to measure differences in TV and fb between forward slumped and upright sitting postures. Spirometry data were collected for each subject over a five-minute period in each of the two sitting postures. TV was calculated using VE and fb data. Results of repeated measures ANOVA demonstrated statistically significant increases in TV and VE in the upright sitting when compared to a slumped sitting posture. Breathing frequency was shown to be not significantly different from one posture to the next. Many have attributed adverse musculoskeletal conditions to poor sitting posture. Results of this study suggest that poor sitting posture may also adversely affect pulmonary function in healthy adults.