ABSTRACT. Illegal game meat hunting in the Serengeti National Park, Tanzania, and adjacent game reserves provides an important source of protein and cash income to local communities. We construct a profitability model that describes the spatial distribution of the economic costs and benefits of illegal hunting in the Serengeti during the late 1980s and early 1990s. Costs included capital investment in hunting weapons, WR, and the opportunity cost of hunting, WO, both held to be constants; and two spatially variable components, the logistic effort of traveling to hunting areas, WL, and the penalties incurred if arrested, WP. Benefit was the expected income from the sale of meat from resident wildlife species. The model suggests: (1) WR is the most important cost. (2) WL is the second most important cost and likely to determine the spatial distribution of hunting activity if hunters seekto minimize costs. (3) WO and WP are of minor importance, the former because alternative sources of income provide low pay, the latter because the overall chance of being arrested is low. (4) WP exceeds WL only in areas close to the boundary of protected areas. (5) Although resident wildlife contributes only a minor share of illegal offtake compared to the migratory herds, hunting resident wildlife is profitable in 68% of the area. This suggests that hunting of resident and migratory wildlife is highly profitable and may explain why the utilization of the target populations has become increasingly unsustainable.