Men's sexual arousal patterns are category-specific: Men typically display significantly greater physiological responses to sexual stimuli depicting members of their preferred gender category. Category-specific patterns of sexual arousal have not been consistently reported in natal women. We used vaginal photoplethysmography to examine patterns of sexual arousal in 11 male-to-female (MtF) transsexuals following sex reassignment surgery (SRS) and in 72 natal women. Subjective arousal was measured with a continuous response lever. Video clips depicting sexual activity between two males, two females, or one male and one female were used as erotic stimuli. All transsexual participants displayed category-specific sexual arousal. Five homosexual transsexual participants (attracted exclusively to males before sex reassignment) showed greater genital and subjective responses to male than to female stimuli, while six nonhomosexual transsexual participants showed the opposite pattern. Vaginal pulse amplitude (VPA) was lower in transsexual participants than in natal women. The mean correlation between VPA and subjective responses was high in nonhomosexual transsexuals, but was significantly lower in homosexual transsexuals and in natal women. One transsexual participant who reported a change in sexual orientation following sex reassignment displayed VPA and subjective responses consistent with her pre-reassignment sexual orientation. We conclude that male-to-female transsexuals display male-typical category-specific sexual arousal following SRS, and that vaginal photoplethysmography is a promising methodology for studying patterns of sexual arousal in postoperative transsexuals.