The National Institute for Occupational Safety and Health (NIOSH) conducted a health hazard evaluation at the Group Health Associates' Western Hills facility in Cincinnati, Ohio. The request listed several instances of water incursion. Reported health problems among employees included headaches, nasal congestion, chronic coughing, three diagnosed cases of chlamydia pneumonia, and an increase in the number of nonspecific illnesses. NIOSH investigators conducted an initial site visit to the office on August 23 and 24, 2000, and a follow-up visit to look at moisture issues on December 14, 2000. The August site visit included a limited ventilation system assessment, measurement of indoor environmental quality indicators (carbon dioxide [CO2], temperature, and relative humidity), moisture measurements, and limited microbial sampling. The environmental evaluation identified problems with temperature and humidity regulation and air delivery. Temperatures ranging from 69 F to 73 F, and relative humidities ranging from 48% to 70% were recorded on the day of sampling. Elevated CO2 concentrations (up to 1540 parts per million) were recorded in the examination rooms, waiting areas, and the Medical Records Department, indicating insufficient ventilation. The ventilation systems' thermostats were located in the perimeter offices where solar load affected the office conditions. Excessive moisture was detected in interior and exterior walls which could be due to water incursion from overflowing toilets and poor humidity control in the building. The visual assessment did not reveal widespread microbial contamination. A sticky tape sample collected beside one of the toilet areas indicated fungal growth. The outside air damper for the original building heating, ventilating, and air-conditioning unit was closed, and there was no provision of outside air to the basement. The major water-incursion issues had been addressed before the initial NIOSH site visit. NIOSH investigators recommend that problems with the regulation of temperature, humidity, and air delivery within the Group Health Associates' Western Hills facility be corrected. It is unclear if these issues were the cause of the reported health symptoms, many of which were non-specific, however, improving the indoor environmental quality should minimize work-related health complaints. The cases of Chlamydia pneumonia are likely caused by person-to-person transmission from respiratory secretions. The occurrence of these cases reinforces the need to practice good personal hygiene in the workplace.