We compared the results of the pulsed-field gel electrophoresis and the sequence-based typing (using the loci flaA, pilE, asd, mip, mompS and proA) for subtyping of L. pneumophila 1 strains isolated from a hospital water supply. Molecular typing was carried out on 61 isolates (41,5% of the positive samples) selected on space and temporal criteria in order to follow the evolution of the water-system colonization. For all 61 isolates, the sequence of the amplified mip gene fragment was 100% identical to Legionella pneumophila strain Wadsworth. Genotype testing by PFGE analysis identified three different patterns, correspondent to three SBT types according to the allelic profiles. Both PFGE and SBT indicated the circulation and the persistence in the hospital potable water-system of three clones variously distributed in space and time. The two molecular methods adopted showed a 100% concordance, although a low degree of genetic heterogeneity characterized the isolates. The electrophoretic patterns were sufficiently unambiguous to consider PFGE a highly discriminatory typing method, but the SBT technique besides accurately characterizing isolates, was able to identify Legionella strains through analysis of the mip gene. A typing method with this level of discriminatory power has great potential for assisting in epidemiological studies.