Tuberculosis is heavily worldwide spreading in the last years. More and more signalations seem to indicate that the incidence of drug-resistant Mycobacteria is increasing in almost all industrialized countries. The authors have carried on a study on the percentage of drug-resistant strains of Mycobacterium Tuberculosis (MT) among isolates from patients affected by active pulmonary tuberculosis hospitalized through the years 1992-94. Out of 59 isolates of MT, 20.3% were drug-resistant: 25% of them to 2 drugs and 16.6% to 3 or more drugs. Resistance to single drug was so distributed: Streptomycin 11.8%, Isoniazid 6.7%, Rifampycin 3.4%, Ethambutol 6.7%, Ansamycin 3.4%, Pyrazinamide 5.0%, Ethionamide 1.7%. These results were confronted with analogous data on MT drug-resistance collected in the same hospital division in the years 1978-82 and 1985-87. The data analysis shows that actual incidence of drug resistant strains of MT is only slightly decreased but quite similar to that observed in 1978-82, except for Ethambutol, while there is a remarkable reduction vs. 1985-87; in that period, in fact, the highest incidence of drug resistance was recorded. The authors' conclusion is that only little differences were observed in the total amount of resistant strains of MT through 20 years; they also outline that resistance to Ansamycin, most recent out of all tested drugs, is quite similar to that observed for Rifampycin, that is chemically analogous.