The purpose of this study was to identify the prevalence of molars with furcation involvements grades II and III in adults participating in the Jonkoping Oral Health Study 2003. The second aim was to study correlations between different variables and the presence of furcation involvement in these individuals. The present study was performed using bitewing and apical radiographs from 329 subjects. Furcations were considered healthy if the furcation was filled with bone up to the fornix. Two thousand fourteen molars fulfilled the inclusion criteria. The prevalence of molars with furcation involvements was 8.3%. Univariate analysis showed that plaque, age, and presence of periodontal pockets were significantly correlated with furcation-involved molar/s (P 0.0001). Gingivitis and education were also significantly correlated to the presence of furcation involvement (P 0.006) and (P <= 0.01), respectively. Gender had no association with presence of involvements. Multivariate analysis showed that age and presence of periodontal pockets were significantly correlated with furcation involvement (P 0.0001). Smoking was also found to be associated with furcation involvement (P 0.04). The tooth most frequently and least likely displaying furcation involvement was the maxillary first molar and the mandibular second molar, respectively. Periodontal pockets, age, and smoking were risk indicators for furcation involvement.