Mitochondrial transfer RNA (mt-tRNA) mutations are the commonest mitochondrial (mtDNA) mutations to cause human disease. The majority of mt-tRNA mutations are heteroplasmic and while some exhibit maternal transmission within families, many others are only seen as sporadic mutations. Using the available clinical, biochemical and genetic data from published pathogenic mt-tRNA mutations, we have explored several different factors thought to influence the transmission of mt-tRNA mutations. Our data show that the most important factor in predicting whether a mutation is transmitted to offspring is whether the mt-tRNA mutation is selected against in a rapidly replicating tissue such as blood. This suggests that those mt-tRNA mutations which exert a major phenotype in dividing cells are unlikely to be inherited. This is entirely compatible with recent observations on the mitochondrial genetic bottleneck in early development and has important implications for families with mt-tRNA disease.