Periodontal bone loss associated with periodontitis results in increase in the distance between the cemento-enamel junction (CEJ) and the alveolar bone crest (ABC). This study analyzed periodontal bone loss in 100 mandibles of South African blacks who were never exposed to preventive or restorative dental treatment. Specimens were equally distributed over the third to the seventh decade of adult life. CEJ-to-ABC (CA) distances were measured along 4904 surfaces of 1076 teeth. Analysis of the measurements showed that, generally, CA distances increased with age; differences were substantial between the first and fifth age groups. The incisors were most severely affected in all age groups, and bone loss was less severe around posterior teeth. Pre-molars and second molars lost the least bone. No significant differences between measurements on the buccal, lingual, mesial, or distal surfaces for these teeth were found. Measurements on the right and left sides of the mandible did not differ significantly. These observations may, in part, have been influenced by mid-life loss of teeth caused by severe periodontitis; their absence from the sample may have masked the true extent of periodontal bone loss. The difference in age of eruption and, therefore, the difference in period of exposure to the oral environment may account for the more severe bone loss in the anterior teeth, especially in specimens from younger individuals (21-30 years).