Management agencies commonly use high minimum length limits for muskellunge Esox masquinongy to achieve the goal of trophy fisheries. Evaluations of length-limit effects on muskellunge populations have been limited. We evaluated the effects of a 40-in minimum length limit (total length) on seven northern Wisconsin lakes and compared the results to eight lakes that remained at the statewide minimum length limit of 32 or 34 in. Five years after its implementation, the 40-in minimum length limit did not increase adult muskellunge abundance or size structure compared with reference lakes. Variation among lakes dictates that low-density species such as muskellunge be monitored for extended periods and that reference waters also be monitored to aid interpretation of data and development of meaningful management recommendations.