Infrastructure development brings immediate and obvious benefits to communities. What isn't as immediately obvious is that such development can also open the way for negative changes---such as the spread of sexually transmitted diseases. This report examines the impact on the local people of an important infrastructure project in northwest Lao People's Democratic Republic---the upgrade of Route 3, which forms part of the Northern Economic Corridor linking Thailand with the People's Republic of China. The report also outlines the implications for future HIV mitigation programs, and recommends ways to ensure that future programs maximize the good that infrastructure development brings and minimize negative impacts.