We examined the influence of age and sex on body composition and organs of lesser scaup (Aythya ajfinis) during mid-winter in southwestern Louisiana. Except for intestine weight, organs and body components were similar in size between adult and immature lesser scaup. Body components and organs of males generally were larger than those of females. Body weights of lesser scaup in our study were lower than those reported from the same area more than 20 years ago. Declines in condition could result in lowered survival or reproductive performance. Information on winter survival is not available, but harvest age-ratio data suggest that recruitment of lesser scaup has declined in the Mississippi Flyway.