There are now validated radiographic indices that can be used by clinical investigators to determine the prevalence and severity of OA of the hand, hip, knee, apophyseal joints of the cervical and lumbar spine, and cervical disc degeneration. Clinical investigators should consult standardized atlases for radiographic index descriptions. The use of an atlas and training sessions improve the agreement between and within readers. The standard global grades developed by Kellgren and Lawrence have been used in epidemiologic studies to determine the prevalence of OA in specific joints. The evaluation of radiographic OA by individual radiographic features allows for the characterization of the variation in radiographic features often found in OA and in degenerative disc disease. Methods have been developed to maintain interrater and intrarater agreement in scoring radiographs. Radiographic indices of OA can now be reliably applied to clinical epidemiologic-based studies of OA.