Molecular studies have been successfully applied in evaluating epidemiological linkages in tuberculosis. A total of 87 isolates of Mycobacterium tuberculosis were collected from patients in all regions of Lebanon and characterized in terms of drug sensitivity. Double-repetitive-element polymerase chain reaction was used to differentiate between strains. Various correlations related to age, sex, region, sensitivity and genotype were examined. Several genotypes were more common in certain age ranges. Male patients appeared more likely either to be infected by or to develop multi-drug resistant strains. There was also evidence for a distribution of genotype groups indicating some level of geographical isolation and hence separate evolution of M. tuberculosis strains.