Aim of the Study:The complex hospital environment requires special attention to ensure a healthy indoor air quality (IAQ) to protect patients and healthcare workers against hospital-acquired infections and occupational diseases. Poor hospital IAQ may cause outbreaks of building-related illness such as headaches, fatigue, eye, and skin irritations, and other symptoms. The general objective for this study was to assess IAQ inside a large University hospital at Al-Khobar City in the Eastern Province of Saudi Arabia.Materials and Methods:Different locations representing areas where most activities and tasks are performed were selected as sampling points for air pollutants in the selected hospital. In addition, several factors were studied to determine those that were most likely to affect the IAQ levels. The temperature and relative percent humidity of different air pollutants were measured simultaneously at each location.Results:The outdoor levels of all air pollutant levels, except volatile organic compounds (VOCs), were higher than the indoor levels which meant that the IAQ inside healthcare facilities (HCFs) were greatly affected by outdoor sources, particularly traffic. The highest levels of total suspended particulates (TSPs) and those less than 10 microns (PM10) inside the selected hospital were found at locations that are characterized with m4ore human activity.Conclusions:Levels of particulate matter (both PM10 and TSP) were higher than the Air Quality Guidelines (AQGs). The highest concentrations of the fungal species recorded were Cladosporium and Penicillium. Education of occupants of HCF on IAQ is critical. They must be informed about the sources and effects of contaminants and the proper operation of the ventilation system.