The objective of the study was to determine the effects of androgen depletion on erectile function in a population of male-to-female transsexuals. The erectile function of 25 consecutive male-to-female transsexuals on androgen depletion treatment and scheduled for surgical gender reassignment was prospectively evaluated using medical and sexual history, physical examination, total serum testosterone, International Index of Erectile Function (IIEF-15) questionnaire, penile colour-coded Doppler ultrasonography (CDU) after pharmacological stimulation and nocturnal penile tumescence (NPT) test. All but one had undetectable or low testosterone. Subjective erectile function, according to IIEF-15 scores, and penile CDU findings did not correlate with testosterone levels, whereas NPT test findings correlated well with testosterone levels. These findings would suggest that nocturnal erections are androgen-dependent whereas sexually induced erections are androgen-independent. It can also be assumed that testosterone is important but not essential for male erectile function and that other androgen-independent pathways can be responsible for sexually induced erections.