Allopreening is a form of social grooming that has not been extensively studied in most birds. Observations of allopreening in Sitta pusilla (Brown-headed Nuthatch) are described where sex, age, and kin relationships were known for the individuals performing the behavior. Young of the year allopreened adults and nest mates, adult male helpers allopreened breeding females and unrelated adults, and breeding adults allopreened one another as well as young of the year. Previous observations suggested allopreening served to maintain pair bonds in the Brown-headed, but these observations suggest the behavior may have expanded functions. Although most allopreening focused on neck and head regions where the behavior may primarily serve hygienic functions, wings and backs also were allopreened frequently in a manner consistent with the social functions suggested for other birds.