Centromeres attach chromosomes to the spindle during mitosis, thereby ensuring the equal distribution of chromosomes into daughter cells. Transcriptionally silent heterochromatin of unknown function is associated with centromeres in many organisms. In the fission yeast Schizosaccharomyces pombe, the silent mating-type loci, centromeres, and telomeres are assembled into silent heterochromatin-like domains. The Swi6 chromodomain protein affects this silencing, and now it is shown that Swi6p localizes with these three chromosomal regions. In cells lacking Swi6p, centromeres lag on the spindle during anaphase and chromosomes are lost at high rates. Thus, Swi6p is located at fission yeast centromeres and is required for their proper function.