OBJECTIVES: To investigate the prevalence of alveolar bone loss around the first permanent molars, and first and second deciduous molars in Australian school-aged children attending the Royal Dental Hospital of Melbourne. METHOD: Nine hundred and ninety-five records were examined for useable bitewing radiographs. From these, radiographs of 542 Australian school children aged 5-12 years were used. The cervical-enamel junction (CEJ) to the alveolar bone crest (ABC) distance was measured using the transparent ruler on the magnifier. Each inter-dental site that was readable was scored as one for the following categories: not available (NA); no bone loss (NBL)- the CEJ-ABC was < or =2 mm; questionable bone loss (QBL): the distance from the CEJ-ABC was >2 and <3 mm; and definite bone loss (DBL): the distance from the CEJ to ABC was > or =3 mm. RESULTS: Seventy-one children (13.0%) were found to have 83 DBL sites, as determined by bone levels >3.0 mm from the CEJ. Seventy children had QBL lesions only, 50 children had DBL only and 21 children had both. The overall prevalence of bone loss was 26%. Second deciduous molars were found to be the most affected teeth with almost 75% lesions being distal. These teeth comprised 50% of the DBL lesions. Children of Asian-Far Eastern origin had a higher percentage of sites with bone loss compared with children of Caucasian origin, being 29.5% and 19.7%, respectively, but lower than that of children of Middle-Eastern origin (35.2%). When the data were analysed with relation to age, there was no relationship between age and prevalence of bone loss. CONCLUSION: In the population studied, there was an overall prevalence of periodontal bone loss of 26% and DBL of 13% in an Australian school-aged group. Calculus was detected infrequently and, where present, was associated with bone loss.