The recently identified insertion element IS6110 is present in most strains of the Mycobacterium tuberculosis complex. Restriction fragment length polymorphism (RFLP) based on IS6110 generates strain specific fingerprints and allows typing of M. tuberculosis strains. We present here the results of a RFLP study on 12 multi drug and 10 single drug resistant, recent isolates of M. tuberculosis received from different clinical microbiology laboratories in Belgian hospitals. All isolates originating from different patients yielded distinct RFLP patterns possessing 2 to 13 copies of IS6110. There was no correlation between the number or location of IS6110 copies and the drug resistance patterns. These results illustrate the existence of a broad polymorphism among Belgian isolates. Though this preliminary study did not reveal an outbreak or a micro-epidemic, we consider that the establishment of a DNA fingerprint bank in Belgium will be extremely helpful for tracing recent sources of infection, for the control of a possible spread of multidrug resistant organisms, and for the surveillance of tuberculosis in general.