Portugal has one of the highest tuberculosis notification rates of the European Union with Lisbon Health Region having an incidence rate well above the national average. The present study analyses the transmission, drug susceptibility and characteristics of a study population from a Central Lisbon's Hospital. One hundred and thirty -two Mycobacterium tuberculosis clinical isolates were previously tested for drug susceptibility to first -line drugs. The multidrug (MDR) resistance rate was found to be 3.0%, while 13.6% of the isolates were resistant to one or more first -line drugs. HIV serology was available for 98 patients, 26 (26.5%) were positive. Genotyping was performed by MIRU -VNTR and 53 (40.2%) out of the 132 isolates were found to be distributed through 17 MIRU -VNTR clusters of two or more isolates. Lisboa strains accounted for 25.8% of all strains. We conclude that transmission of resistant and susceptible Mycobacterium tuberculosis strains is occurring, with special concern for Lisboa strains.