The introduction of Brown Tree Snakes (BTS; Boiga irregularis) on Guam has had devastating impacts on native wildlife and human infrastructure, resulting in concerted efforts to control populations and prevent the spread of this invasive species to other islands. These control efforts, particularly aerial drops of acetaminophen, can eradicate BTS within target areas, but snakes can repopulate those areas via compensatory immigration. Therefore, understanding how gene flow corresponds to dispersal can add critical information for maximizing effectiveness of control efforts. To examine dispersal patterns of BTS on Guam from a genetics perspective, we genotyped 332 individual snakes at 22 microsatellite loci to test for the presence of physical barriers (e.g., roads) and spatial genetic structure associated with restricted dispersal. Brown Tree Snakes experience sufficient gene flow on Guam to resist any strong physical barriers, a likely interaction between their large population size and ability to cross physical obstacles such as roads. In addition, BTS exhibited isolation-by-distance across the entire study area, but those captured on Andersen Air Force Base in northern Guam appeared to disperse randomly regardless of sex. Overall, BTS experience high gene flow across Guam, particularly in less urbanized areas in northern Guam. Therefore, compensatory immigration will likely make complete eradication difficult without antisnake barriers.