OBJECTIVE: The introduction of molecular typing methods in the 1990s to study the epidemiology of tuberculosis (TB) has significantly improved the possibilities of quantifying transmission of Mycobacterium tuberculosis in different human settings. The purpose of this study was to investigate transmission of TB in 35 family-households in Poland. METHODS: Two PCR-based genotyping methods: spoligotyping and mycobacterial interspersed repetitive unit-variable number of tandem repeats (MIRU-VNTR) typing were used. RESULTS: Of 78 patients, 49 (63%), could be assigned to intra-household transmission on the basis of identical DNA fingerprints upon a combined typing approach. However, if a single spoligotype spacer or a single MIRU-VNTR locus variation was tolerated in the cluster definition, the intra-household transmission raised to 85% of all patients. For 12 patients in 6 households, the M. tuberculosis isolates were clearly distinct in either spoligotyping or VNTR typing or in both genotyping methods, suggesting that these patients were infected by the sources in the community. CONCLUSIONS: This study is the first to provide the results of a molecular epidemiological investigation performed within family-households in Poland. It shows the household setting as an important reservoir of M. tuberculosis transmission, and thus argues in favor of routine and extensive screening of the family contacts of TB patients.