The dry rot fungus Serpula lacrymans is known as one of the most aggressive fungal house invaders in temperate regions. Recent genetic and phylogeographic studies have shed light on the distribution, colonisation and population structure of S. lacrymans on a broader, global scale. Yet, even though S. lacrymans have been long known by both unfortunate house owners and researchers, little is still known about its population structure on a smaller scale, including within buildings. Therefore, a combination of vegetative compatibility tests and molecular techniques were used to investigate the indoor distribution of S. lacrymans in six houses in Norway. Vegetative compatibility experiments corroborated earlier findings that vegetative compatibility not necessarily corresponds to the same individual (genet) of S. lacrymans, as different genets often display the same VC group affiliation. The results also indicate that infections in Norway often are made up of a single genet with the ability to colonise an entire house. Interestingly, the molecular investigations indicated that some of the genets stem from parents with identical mating genotype. However, this is probably more likely a result of low levels of molecular variation in the analysed markers. I also speculate that this observation may be caused by same-sex mating in S. lacrymans, a recently discovered form of homothallism in fungi. The presence of a formerly unrecognised MAT B allele is also indicated by the molecular data.