In 1964, Hamilton formalized the idea of kin selection to explain the evolution of altruistic behaviours. Since then, numerous examples from a diverse array of taxa have shown that seemingly altruistic actions towards close relatives are a common phenomenon. Although many species use kin recognition to direct altruistic behaviours preferentially towards relatives, this important aspect of social biology is less well understood theoretically. I extend Hamilton's classic work by defining the conditions for the evolution of kin–irected altruism when recognizers are permitted to make acceptance (type I) and rejection (type II) errors in the identification of social partners with respect to kinship. The effect of errors in recognition on the evolution of kin–directed altruism depends on whether the population initially consists of unconditional altruists or non-altruists (i.e. alternative forms of non–recognizers). Factors affecting the level of these error rates themselves, their evolution and their long–term stability are discussed.