The raccoon (Procyon lotor) is the definitive host of Baylisascaris procyonis, a large intestinal roundworm. The prevalence of infection among raccoon populations often is high, and in the midwestern United States B. procyonis is documented in 68–82% of raccoons. Because raccoon populations appear to be increasing in response to changes in human land use and because B. procyonis is considered an emerging zoonotic disease, it is important to determine reliable methods to monitor prevalence of infection among raccoons. We compared the relative sensitivity of 3 common methods used by wildlife biologists to determine prevalence in free-ranging raccoon populations. We determined prevalence of infection among midwestern raccoon populations from 456 raccoon fecal samples, 742 raccoon latrine samples, and 212 necropsies (gut analysis). We developed logistic regression models in order to predict the log likelihood of presence of B. procyonis in a given sample as a function of season, land use, and technique. Finally, we measured the sensitivity of fecal sampling by evaluating fecal samples taken from 72 necropsies for the presence of B. procyonis eggs. Necropsy analysis yielded the highest measure of prevalence (44%), followed by latrine samples (22.5%), and fecal samples (17.5%). Necropsy analysis explained the most variance in logistic models, suggesting that this is the most reliable method. However, this technique is labor-intensive and may not be the most efficient method for large-scale investigations of B. procyonis prevalence. Fecal analysis is a reliable method of determining prevalence among raccoons as we observed B. procyonis eggs in 66% of fecal samples taken from positive necropsies. Latrine sampling may be the most efficient method and perhaps the best estimator of zoonotic potential; however, wildlife managers should realize that this measure often is an underestimate of prevalence among raccoons and develop management plans accordingly.