In advanced periodontal disease alveolar bone crestal loss is readily apparent on radiographs. However, in incipient disease there is a lack of consensus regarding what constitutes crestal bone loss on a radiograph. To properly assess crestal bone loss radiographically requires an appropriate base of reference indicative of the absence of destructive periodontal disease. In this study the radiographic CEJ-crest distance as a measure of crest height was determined for sites at which clinical attachment measurements indicate no attachment loss. From these measurements it is concluded that no crestal bone loss is consistent with a range of radiographic CEJ-crest distance between 0.4 and 1.9 mm (95% confidence limits) as evidenced on bite-wings.