Feather-chewing lice (Order Phthiraptera, Suborder Ischnocera) commonly infest birds and may affect their survival and reproduction. From 1993 to 2005, we examined several aspects of the biology of breeding Tree Swallows (Tachycineta bicolor) potentially associated with holes in wing and tail feathers caused by feather-chewing lice. Most individuals had <10 feather holes, but 90% of second-year (SY) females, 68% of after-second-year (ASY) females, and 80% of males had ≥1 feather hole. ASY females had significantly fewer feather holes than SY females and males. There was evidence of positive assortative mating for feather hole number between ASY females and their mates. SY females and their mates did not differ significantly in the number of feather holes, but ASY females had significantly fewer holes than their mates. Males with fewer feather holes were heavier and had longer right wings. Feather hole abundance was not significantly associated with reproductive performance. Feather hole abundance was not associated with whether females bred 1 time or >1 time at our study site, but males with fewer holes were more likely to breed >1 time. Mean feather hole abundance differed significantly among years for SY females and males that bred 3 and 4 times, respectively, but not for ASY females that bred 4 times. Collectively, these data suggest that feather-chewing lice, as estimated by the damage they cause to wing and tail flight feathers, have little effect on Tree Swallow fitness.