HIV prevention has focused on reducing the chances of transmission of the pathogen via sexual transmission. We argue that current pressures to persuade people that "abstinence" is a reasonable programme goal are based on misapprehension as to the balance between environmental and contextual factors and individual choices in determining why and how people have sex. Continuing insistence on the part of major prevention programme funders that changing behaviour alone--rather than changing its context--is the main problem will result in poor policy choices. It is particularly important to get these choices right at a time when increased amounts of money are becoming available for engagement with the HIV/AIDS epidemic. Failure to take account of this problem may have results beyond the field of HIV prevention.