Substantial mortality attributable to infection with Parelaphostrongylus tenuis was reported in 2 herds of blackbuck antelope (Antelope cervicapra) in southwestern Louisiana. Both herds had outbreaks in which all affected antelope had neurologic disease and subsequently died. Affected antelope were anorectic and weak. They staggered, trembled, isolated themselves from the herd, became recumbent, and, possibly, were blind. In 1 herd, 6 of 27 antelope were affected, and in the second herd, 7 antelope were affected. Both herds were on farms that raised various native and imported ruminants, including white-tailed deer. None of the remaining ruminants was affected during these outbreaks, and subsequent outbreaks have not been reported. Four antelope and the brain of a fifth antelope were submitted for postmortem examination. Meningeal worms were identified grossly in only 1 antelope. Metastrongyloid nematodes were detected histologically in 3 antelope. The amount and extent of inflammation varied greatly among affected antelope.