Abstract In Britain surnames are paternally inherited and they are thus analogous to the paternally inherited Y chromosome. Therefore, males who share surnames might be expected to share Y-chromosomes. However, this simple relationship is complicated by the multiple origins of many surnames, non-paternity, and mutations on the Y chromosome. Y-chromosomal DNA polymorphisms provide us with a set of tools to directly test, at a molecular level, this hypothetical link. Since surnames are highly geographically localized, local geographical patterning of Y haplotypes is a potential confounding factor: genetic structure within names could arise as a result of geographical structure within Britain, rather than due to descent. Geographical structure was examined using samples from this research but little evidence of such structure was found. Then, to ask if a signal of haplotype sharing exists within surnames, 150 pairs of men were recruited, each sharing a British surname, and Y-haplotype sharing assessed within each pair. The signal of coancestry exhibited constituted powerful evidence for common origins of men sharing surnames. It also has forensic implications and this research shows that it could allow the prediction of surname from crime-scene samples. . These findings for pairs of men sharing surnames suggested that a larger scale' study of larger sample sizes would be worthwhile, so a set of 40 surnames with an average sample size of 42 apparently unrelated men was investigated using Y markers. Correlations between surname rank and degree of diversity exist: the more common the surname, the greater the diversity of Y-chromosomal haplotypes associated with the name. Furthermore, an individual is far more likely to share a Y-chromosome haplotype with another person sharing their surname if the surname is rare. While a handful of surnames show some evidence of having a single founder, overall the picture is one of far more complex surnames histories.