The devastating dry rot fungus, Serpula lacrymans, has a worldwide occurrence in buildings. We investigated the genetic variation in European isolates belonging to five vegetative compatibility groups (VCGs) by AFLP analysis. Our results indicate that S. lacrymans in Europe is genetically extremely homogenous; only five out of 308 scored AFLP fragments (1.6%) were polymorphic. In contrast, S. himantioides, the closest relative of S. lacrymans, possessed 31.3% polymorphic fragments (84 out of 268). AFLP polymorphisms observed in S. lacrymans were distributed independently of the VCG boundaries, indicating that the VCGs do not represent clones but that different genets of S. lacrymans frequently share similar vic alleles due to low genetic variation. Thus, although the European S. lacrymans is genetically extremely homogeneous, and our results suggest that the species reproduces and spreads mainly sexually and not by clones.