Haemonchosis concomitant with malnutrition has been a frequent parasitic disease observed in white-tailed deer (Odocoileus virginianus) in the southeastern United States. Typically, afflicted deer were fawns from the southeastern coastal plain, and most cases were submitted between October and March. A survey of deer from 14 areas along the Atlantic coast revealed that fawns had significantly higher numbers of Haemonchus contortus than adults and in some areas fawns harbored H. contortus burdens that were considered pathogenic. The lower H. contortus burdens in adult deer suggested a naturally-acquired immunity. This hypothesis was supported by a trial in which challenge of small groups of Haemonchus-naive and previously exposed penned deer resulted in poorer performance of H. contortus in previously exposed deer. This study indicated that during their first winter fawns are particularly vulnerable to a haemonchosis/malnutrition syndrome.