The concentration levels of airborne bacteria were measured in clinical/hospital rooms in Upper Silesia , Poland, in buildings of varying conditions. It was found that the typical level of bacterial aerosol concentration is about 10³ CFUm^-3 in clinical outpatient rooms and ranges from 10² CFUm^-3 to 10³ CFUm^-3 in hospitals, depending on the number of occupants and physical quality of the building. The increased level of the airborne bacteria in patient rooms resulting from bed-making was noticed. The Staphylococcus/Micrococcus group was a dominating part of the bacteria in studied hospitals/clinic air, contributing together 58-78% of the total bacteria concentration, confirming that detected airborne bacteria mainly originated from human organisms. The size distributions of bacterial aerosol in naturally ventilated rooms have peaks in the size range between 1.1 and 3.3 µm while in the mechanically ventilated hospital rooms with HVAC the peak appears in the diameter range from 3.3 µm to 4.7 µm.