An outbreak of ascaridiasis occurred in 10-wk-old guinea fowl (Numida meleagris) on a commercial farm. Birds had exhibited elevated mortality (11.66%) in the previous week, as well as increased water consumption, weakness, anorexia, and stunted growth. Numerous nematodes, occasionally occluding the intestinal lumen, were present in the jejunum and ileum and were identified as Ascaridia numidae based on microscopic morphology. Ribosomal DNA 18S and 28S D3 sequences of the nematode were deposited into GenBank and found to be most similar to Ascaridia galli and Toxocara vitulorum, respectively; sequences for A. numidae had not been previously reported. Treatment with piperazine sulfate significantly reduced the number of adult worms in the intestines, greatly decreased eggs per gram of feces, relieved clinical signs in the flock, and returned the flock mortality back to expected levels. All findings implicate A. numidae as the cause of elevated mortality in this flock.