Corner stores are part of the urban food environment that may contribute to obesity and diet-related diseases, particularly for low-income and minority children. The snack foods available in corner stores may be a particularly important aspect of an urban child's food environment. Unfortunately, there is little data on exactly what snack foods corner stores stock, or where these foods come from. We evaluated snack foods in 17 Philadelphia corner stores, located in three ethnically distinct, low-income school neighborhoods. We recorded the manufacturer, calories, fat, sugar, and sodium for all snack items, excluding candy and prepared foods. We then compared the nutritive content of assessed snack items to established dietary recommendations and a school nutrition standard. In total, stores stocked 452 kinds of snacks, with only 15% of items common between all three neighborhoods. Total and unique snacks and snack food manufacturers varied by neighborhood, but distributions in snack type varied negligibly: overall, there were no fruit snacks, no vegetable snacks, and only 3.6% of all snacks (by liberal definition) were whole grain. The remainder (96.4% of snacks) was highly processed foods. Five of 65 manufacturers supplied 73.4% of all kinds of snack foods. Depending on serving size definition, 80.0-91.5% of snack foods were "unhealthy" (by the school nutrition standard), including seven of 11 wholegrain products. A single snack item could supply 6-14% of a day's recommended calories, fat, sugar, and sodium on average (or 56-169% at the extreme) for a "typical" child. We conclude that corner store snack food inventories are almost entirely unhealthful, and we discuss possible implications and next steps for research and intervention.