Sexual and social network analysis have been proposed as novel sexually transmitted disease control and research tools. Here, the concordance between chlamydia genotype data and a large sexual network constructed from routinely collected contact tracing data was examined. A sexual network was constructed for Manitoba, Canada, from province-wide contact tracing data. Positive chlamydia specimens from the same time period were collected and genotyped by omp1 DNA sequencing. A high degree of concordance was found between transmission events, on the basis of molecular data, and proposed transmission events, on the basis of sexual network data. Discordant results appeared to occur when a portion of the network contained potential core group members or in areas where contact tracing is difficult to carry out. The agreement between the molecular and epidemiologic data suggests that the use of routine contact tracing data is a valid approach for the construction of sexual networks.