The present study examined men and women's sexual and affective responses to erotic film clips that were combined with different fantasy instructions. Men (n = 29) and women (n = 28) were presented with two types of erotic films (explicit vs. romantic) and two fantasy instructions (fantasizing about one's real-life partner vs. fantasizing about someone else). Genital response, subjective sexual arousal, and affective responses were assessed. Sexually explicit stimuli resulted in larger genital responses; women reported higher subjective sexual arousal than men; and fantasizing about one's partner resulted, overall, in higher subjective sexual arousal and higher levels of positive affect. Moreover, in women, the instruction to fantasize about one's partner resulted in stronger subjective sexual arousal to the explicit film than the instruction to fantasize about someone else. Results suggested that physiological, subjective, and affective responses to erotic film stimuli are impacted not only by stimulus characteristics but also by the viewer's interpretation of the depicted relationship.