Irregular migration to Europe by sea, though risky, remains one of the most popular migration options for many Sub-Saharan Africans. This study examines the drivers of irregular migration decisions using an incentivized lab-in-the-field experiment in rural Gambia, the African country with the highest per-capita rate of irregular migration to Europe. Potential migrants substantially overestimate the probability of dying en route, reporting an average belief of 51 percent compared with a best available estimate of about 20 percent. In the experiment, reducing the probability of dying en route from 50 to 20 percent raises willingness to migrate irregularly by 3.0 percentage points, while reducing the probability of obtaining legal residence from 50 to 30 percent lowers it by 2.1 points. Our results highlight the importance of potential migrants' prior beliefs in shaping responses to information and suggest that information policies that fail to account for these beliefs may backfire.