The reproductive strategies of species of non-indigenous crayfish make an important issue in astacological research. Although crayfish reproduction has been well studied, there is little information available on the occurrence of intersexuality. We report the first evidence of intersex in the signal crayfish, Pacifastacus leniusculus (Dana, 1852). An intersexual specimen was found among five tested signal crayfish. Morphology revealed both male and female genital openings, as well as male gonopods. The specimen superficially appeared male but contained both testes and ovaries, with an atypical dispersed structure. Sperm was obtained from this crayfish. Histology showed both spermatocytes and oocytes. The gonadosomatic index (GSI = 3.79) was considered as a morphometric parameter of the intersexual crayfish. The ova present in the intersex male raised its GSI to the three-fold of that of normal males.