Multiresistant tuberculosis (MDR), defined as Mycobacterium tuberculosis resistant to isoniazid and rifampicin, is a growing problem worldwide. In year 2000 it was estimated that an average of 3.2 % of all new cases of tuberculosis were multiresistant. The World Health Organisation (WHO) has focused on this problem, and studied its prevalence throughout the world. Some countries are defined as hotspots , meaning that primary MDR makes up a prevalence greater than 3 %. Hotspot countries include Russia, Latvia, Estonia, the Dominique-Republic and parts of India and China. One of the most important reasons for the development of MDR is the use of monotherapy. WHO has developed a treatment strategy, Direct Observed Treatment (DOT), which is recommended for worlwide implementation. At the National Institute of Public Health all isolates of M.tuberculosis in Norway are genetically analyzed. They use DNA-fingerprinting to identify the different isolates. A probe specific for a M.tuberculosis-sequence, IS6110, is used. 17 patients were treated for multiresistant tuberculosis at Ullevål Universitetssykehus in the period 1994 2002. There are no Norwegians among the 17 patients with MDR. 12 of the 17 patients at Ullevål had the same IS6110-pattern, and therefore the same isolate. I found two clusters among these 12 patients, one with 6 patients and one with 4 patients. Two patients I couldn t find in any cluster. Most likely there is a link between all the patients with the same IS6110-sequence. One of these patients developed MDR during treatment in Norway, and eleven patients were most likely infected by transmission of the MDR strain developed by this patient. One other patient also developed MDR during treatment in Norway. Four patients probably brought their MDR strains with them upon arrival in Norway.