The present study describes the prevalence of alveolar bone loss (ABL) in children in relation to caries, contact and space loss. In addition, the microbial composition of the subgingival plaque of 20 sites, from 5 children, is presented. Bite-wing radiographs from 500 children were examined. ABL was evident in: 99 sites from 60 children; > 1 site in 27 children; the maxilla only in 34 children; the mandible only in 17 children; both arches in 9 children; 37 sites with no caries; 4.9 percent of all sites with proximal caries; 15.8 percent of all sites with contact loss; and 20.5 percent of all sites with mesial drift. Anaerobic bacteria were cultured from all 20 sites. No significant differences in the percentages of colony forming units of Actinobacillus actinomycetemcomitans and black pigmented Bacteroides were found among sites with/without bone loss, with/without caries or probing depths smaller/equal or larger than 2.5 mm.