Summary: Congress has questioned whether beneficiaries of the military's health maintenance organization--TRICARE Prime--are able to schedule timely appointments for care. GAO found that 70 percent of appointments for a routine visit at a military treatment facility were scheduled within the Defense Department's (DOD) timeliness standard and that 80 to 97 percent of appointments for acute or preventive care or for specialists were so scheduled. Active duty military and other enrollees may not obtain appointments within DOD's standard because enrollees sometimes request a date later than one offered within the standard, DOD permits nonenrollees to make appointments and obtain care at the facilities, and military beneficiaries traditionally use health care at a higher rate than do private-sector beneficiaries. DOD's current tools for measuring appointment timeliness are inadequate, although it is attempting to improve them. GAO recommends that DOD modify and use its Composite Health Care System instead of its Customer Satisfaction Survey and report the results at all levels. DOD should also test a policy for canceling appointments for nonenrollees when active military or other TRICARE Prime enrollees request care.