The focus of research in animal buildings has always been on the measured concentrations of contaminants the workers and animals are exposed to; emission measurements have only gained attention in recent years due to potential government regulations on air quality emissions from animal feeding operations (AFO). The contribution of AFO to ambient PM10 and PM2.5 entails reliable measurement of particle size distribution. The size distributions of airborne dust at multiple locations indoors and at the exhaust of a wean-to-finish swine building in Illinois were measured by collecting total suspended particulate matter on Teflon filters. The Horiba LA-300 light scattering particle distribution analyzer was used for particle size distribution analyses. Results showed that the mass median diameter (MMD) of swine dust at the exhaust was lower by about 14% than the average MMD indoors (26.84 vs. 31.55 μm), while the geometric standard deviations were about the same (1.85 vs. 1.86). In addition, the average percentage by volume of PM 10 indoors was about 8% while the percentage of PM10 leaving the building was 10%. In terms of the mass concentrations, PM 10 indoors ranged from 0.014 to 0.125 mg/m3 while at the exhaust PM10 ranged from 0.02 to 0.15mg/m3.