Salmonella enterica serotype Typhimurium has a very large diffusion worldwide within human and non-human hosts. The simultaneous circulation in the same geographical areas of many bacterial clones requires the use of reliable, reproducible and highly discriminatory typing techniques for epidemiological studies. Molecular biological methods, such as plasmid profile analysis, restriction endonuclease digestion of plasmid and chromosomal DNA and hybridization-based procedures have proven to be useful tools for strain differentiation. More recently, detection of polymorphisms in the intergenic spacer regions of rRNA genes by polymerase chain reaction (PCR ribotyping) has been successfully applied to characterize bacterial strains. In this study, PCR ribotyping was performed on 45 epidemiologically related and unrelated strains of S. enterica serotype Typhimurium isolated in northern and southern Italy during 1992. Isolates were simultaneously characterized by traditional ribotyping. Results suggest that PCR ribotyping is a rapid, easy-to-perform and reproducible typing method able to determine relatedness among isolates of this serotype.