The purpose of the study was to determine the bilateral occurrence of dental caries in 12-13 year old and 15-19 year old Saudi school children. There were 673 children (324 boys and 349 girls) in the 12-13 year old group and 734 children (399 boys and 335 girls) in the 15-19 year old group with mean ages of 13.1 (SD 0.7) years and 16.4 (SD 1.2) years, respectively. All children were examined for dental caries using the World Health Organization (WHO) criteria for the diagnosis of dental caries. There were no significant differences between the caries prevalence of right and left sides for most teeth at the significance level of 0.05. Among 12-13 year old children, maxillary first molars (86.5%), mandibular central incisors (86.2%), and mandibular first molars (86.0%) showed very high (p <.01) caries bilaterality. Among the 15-19 year old children, mandibular first molars (91.6%), maxillary first molars (87.9%), and mandibular second molars (79.9%) showed very high (p <.01) caries bilaterality. The conditional probability for bilateral occurrence of caries was highest in first molars followed by second molars and central incisors. The bilateral caries occurrence and conditional probability for bilateral caries occurrence were significantly higher (p <.05) in 15-19 year old children as compared to 12-13 year old children. It was concluded caries bilaterality and the conditional probability for bilateral caries occurrence was high in the study population.