The problem of intersexuality was studied in the freshwater crayfish Samastacus spinifrons by examination of sexual characters of 1,114 specimens captured at nine fluvial populations and a lake population in southern Chile. The existence of this phenomenon was verified in the populations of rivers Contaco, Forrahue, Chico, and Hueyusca. In the first three cases, the percentage of intersexes was 1.5%, 2.7%, and 12.5%, respectively, and in the fourth case it ranged between 0% and 9.8%. A total of 41 intersex specimens was captured in which six gonopore patterns were identified. The dissections showed that 30 of them had testes, seven had ootestes, and four had ovaries. Moreover, all had gonoducts of both sexes, except for one of those with testes which had only sperm ducts, and one of those with ovaries that had only oviducts. It was also found that all intersex specimens had an abdomen with masculine morphological characteristics. This evidence, added to those found in the literature, confirm that in river populations of S. spinifrons, there is a variable percentage of intersex individuals, probably corresponding to transitional stages of a sex change from male to female.