Six juvenile male, one adult male, and three adult female African lions (Panthera leo) from Etosha National Park, Republic of Namibia were presented for necropsy. Two of four adults and one of six juveniles had moderate numbers of gastric spiral bacteria. Additionally, four of four adults had sarcocysts. All juveniles had enteric Sarcocystis sp. oocysts, but no sarcocysts. The gastric spiral bacteria were located extracellularly in fundic and pyloric glands, and also apparently intracellularly within parietal cells in the fundic region. The organisms were 4 to 8 μm long, 0.63 μm wide, with a periodicity of 0.60 μm. The bacteria had blunted ends with multiple flagella. No periplasmic fibrils were observed. The histologic and ultrastructural characteristics of the bacteria were considered most consistent with species in the genus Helicobacter or incompletely identified Helicobacter-like organisms. Gastric inflammation did not differ significantly between infected and uninfected individuals. The bacteria may be commensals, or an opportunistic pathogen. The sarcocysts were observed in hindlimb skeletal muscle of four individuals, with one individual also containing a single sarcocyst within glossal musculature. All observed cysts were mature, and were contained within individual myocytes. The cyst wall consisted of a 44 to 66 nm, granular, electron dense parasitophorous membrane with subjacent, 0.8 to 1.3 μm thick, granular and fibrillar ground substance which also extended into the cyst interior as thin septa. The membrane was folded and lined irregularly spaced, 0.8 to 1.3 μm tall villi centrally containing ground substance. The membrane was continuous in the villar projections, but divided into discrete aggregations of the electron dense material between the villi. Bradyzoites within the interior of the cyst were 3 by 12 μm. The sarcocysts were determined to be Sarcocystis felis based on the characteristic ultrastructural appearance of the cyst wall.