On October 11, 2007, NIOSH received a request for an HHE from the management of the NASA GRC in Cleveland, Ohio, regarding ongoing employee and union concerns about a possible higher rate of cancer among current and former employees of Buildings 500 and 501. This was the second HHE request NIOSH had received regarding this issue. The first request, received in 2004, was also submitted by management. In response to the first request, NIOSH investigators identified no hazardous exposures and closed the HHE with a letter [NIOSH 2004]. In this latest request, NASA GRC management explained that cancer concerns had resurfaced, no cause for these cancers had been identified, and employees were concerned about potential exposure to jet fuel and deicing compounds from the nearby airport, asbestos in the buildings, water damage in the buildings, and general IEQ. This evaluation focused on the employees in Buildings 500 and 501, adjacent three-story brick office buildings constructed in the early 1960s. Building 500 has approximately 110,000 square feet of office space, and Building 501 has about 25,000 square feet; neither building has research labs. Both buildings are on the NASA GRC campus and across the road from the Cleveland Hopkins International Airport. We reviewed reports provided by NASA GRC management concerning asbestos remediation in these buildings, responses to complaints from building occupants, and environmental sampling during the past 14 years. We evaluated surveys about cancer diagnoses from current and former employees in Buildings 500 and 501 that were provided to us by LESA and NASA management. Additionally, a supervisor sent a confidential list of employees with cancer, and the NASA GRC human resources office provided a list of medical and regular retirements from the buildings during the past 5 years. We spoke with representatives from the Ohio Environmental Protection Agency regarding any past or current environmental contamination issues involving Buildings 500 and 501. We also consulted with representatives from the Ohio Department of Health’s cancer registry. We visited the site on October 7-8, 2008. On October 7, 2008, we held an opening meeting with representatives of management and LESA, then walked through the buildings, took measurements of IEQ comfort parameters, and looked for evidence of water damage, water incursion, visible mold, and other potential IEQ problems. On October 8, 2008, we gave two presentations to employees regarding the findings of our evaluation of the cancers reported among employees, and then had a closing conference with representatives of management and LESA. Twenty different types of cancer were diagnosed among employees of Buildings 500 and 501 since 1985. The most common types of cancer diagnosed were breast (17 cases), lung (7 cases), and prostate (4 cases), which are the three most common cancers in the United States. The other types of cancer diagnosed were melanoma, nonmelanoma skin cancer, colon, thyroid, bladder, pancreatic, cervical, uterine, head and neck, bile duct, brain, and stomach cancers; Hodgkin lymphoma, non-Hodgkin lymphoma, clear cell sarcoma, leukemia; and one unknown primary. We found that airport runoff of jet fuel and deicing fluid had entered the Rocky River, which runs next to Building 500. However, jet fuel and deicing fluids are not known to cause cancer, and the river was not a source of drinking water for building occupants, who are supplied with city water. Much of the asbestos in Buildings 500 and 501 had been removed over the years, but some was still managed in place and posed no hazard to building occupants. We identified minor IEQ problems, such as water damage to ceiling tiles and walls, and in some cases poor maintenance of fan coil units, but these are not associated with the cancers that were diagnosed among employees of Buildings 500 and 501. We found no evidence that the cancers reported are associated with work in Buildings 500 and 501 because the number and types of cancers do not appear unusual, the different types of cancers do not suggest a common exposure, no significant hazardous exposures were identified, and evidence leads to nonoccupational causes. Although we recommend no further investigation into the cancers reported in these buildings, employees may have concerns about their own risk for cancer. Therefore, management and the union should take this opportunity to encourage employees to learn about known cancer risk factors, measures they can take to reduce their risk for preventable cancers, and availability of cancer screening programs for certain types of cancer.