The U.S hog production industry has been continually subjected to rapid structural changes since the early 1990s. The industry's move towards more concentrated large hog farms and geographical concentration of such farms, have triggered public concerns over the dangers such big animal feeding operations are likely to pose to the waters of the country. This study investigates the implications of state-level environmental regulations on the structure of hog farms. The results of this study suggest that environmental regulations will result in one of three possible scenarios: (1) a more competitive industry in which small hog operations are not adversely affected which will allow more small operations to enter rather than exit the industry; (2) a more concentrated hog production industry in which large operations survive while small operations exit the industry; (3) no change in the structure of the industry where both sizes of operations are not significantly affected by environmental stringency.