This study compared the effectiveness of 4 videotaped educational programs designed to motivate HIV testing among low-income, ethnic minority women. Four hundred eighty women were assigned randomly to watch one of 2 gain-framed or 2 loss-framed videos. Consistent with prospect theory, participants' perceptions of the certainty of the outcome of an HIV test moderated the effects of framing on self-reported testing behavior 6 months after video exposure. Among participants who reported being certain of the test's outcome, those who saw a gain-framed video reported a higher rate of testing than those who saw a loss-framed message. Among women who perceived the outcome of HIV testing as relatively uncertain, gain- and loss-framed videos led to similar rates of self-reported testing, with some advantage for the loss-framed message.