This investigation was concerned with the incidence and degree of infection by <i>P. tenuis</i> in western Virginia deer herds (<i>Odocoileus virginianus</i>). Relatively little research has been done on <i>P. tenuis</i> in Virginia, especially in the western portion of the state. The objectives of this study were (1) to determine the distribution of pneumostrongylids in the White-tailed Deer in 7 western Virginia counties and (2) to correlate incidence and degree of infection by pneumostrongylids with deer age, sex, geographic location, and physical condition. Specimens were collected from Shenandoah Augusta, Bath, Rockrbidge, Botetourt, Giles, and Craig Counties. Collections were made on the first day of the 1963 deer season. Biologists and students from the department of Forestry and Wildlife at V.P.I and the Virginia Commission of Game and Inland Fisheries collected deer heads from hunters at check stations. A sample of 369 heads of both sexes was obtained. Three-hundred and nine deer heads, 230 does and 79 bucks, were examined for <i>P. tenuis</i>. Seventy-three per cent were infected. The majority of the worms (68%) were found on the dorsal surface of the brain. Overall range of infection was 1-13 worms. In addition, lung and fecal specimens were collected. Fifty per cent of the lung specimens were infected, but no larvae were found in the fecal material. There appears to be an equal likelihood of infection by <i>P. tenuis</i> in deer of either sex less than 1-1/2 years of age. There is also no difference between sexes in the severity of infections in deer less than 1-1/2 years old. Deer of either sex older than 3-1/2 years also have an equal likelihood of infection by <i>P. tenuis</i>, but females between 1-1/2 and 3-1/2 years are more likely to be infected than males. Females older than 1-1/2 years of age had significantly more worms per infection than males of the same age. There is no relationship between weight and incidence of infection in deer less than 1-1/2 years old or older than 3-1/2 years. However, a relationship does exist between the weight of the 1-1/2 to 3-1/2 years age group and the incidence of infection I nthat the heavier deer are more likely to be infected. The deer less than 1-1/2 years of age have lower incidence of infection than older deer and have fewer worms per infection than older deer. There was a significant difference in the incidence of infection between surveyed counties; however, there is no statiscally significant difference between counties and the severity of infections. Further research concerning pathogenic effects of <i>P. tenuis</i> on the White-tailed Deer is imperative prior to employment of any control methods. <i>P. tenuis.</i> may be a serious pathogen, but this research indicates that the deer-<i>P. tenuis</i> relationship is a relatively stable and common association with deer populations seldom adversely affected by the parasites. / M.S.