We studied mate and site fidelity between years in an English population of blackbirds (Turdus merula) from 1985 to 1991. Divorce was observed in 32% of 183 cases where mates had survived from the previous breeding season. After divorces, females tended to nest farther from their original site than males did, but there was no sex difference in distance moved after the death of a mate. The mean annual fledgling production of 60 m x 60 m breeding sites was statistically repeatable among years, even after accounting for possible differences in reproductive performance among site-tenacious individuals. Divorce rates were greatest in low-quality sites. We found no annual fitness cost associated with mating with an unfamiliar bird. However, breeding in a new site cost on average one fledgling per year.