Summary: Pursuant to a congressional request, GAO reviewed the status of the National Aeronautics and Space Administration's (NASA) agencywide environmental compliance and restoration program, focusing on the: (1) NASA hazardous waste sites inventory; and (2) preliminary cost estimate for NASA remediation activities. GAO noted that: (1) NASA has undertaken several initiatives to improve the management of its environmental restoration and compliance program; (2) NASA has developed an environmental strategic plan, established an environmental management division at the headquarters level, identified potential hazardous waste sites, and completed environmental assessments at its major facilities; (3) the program lacks implementation schedules, and if current funding levels continue, the cleanup effort could take longer than NASA predicts; (4) the preliminary estimate to clean up the 650 NASA potential hazardous waste sites is almost $2 billion, and agency officials predict it will take at least 20 years to complete the remedial action phase; and (5) the preliminary cost estimate is likely to increase substantially as more accurate data become available.