Anastrepha fraterculus (Wiedemann) has been reported to show extensive morphological variation along its geographic distribution and is currently recognized as a complex of cryptic species composed of at least eight different morphotypes. The Brazilian-1 morphotype includes the Argentinean and southern Brazilian populations. To contribute with basic information on the distribution of A. fraterculus morphotypes, the sexual compatibility between a Uruguayan and an Argentinean population was evaluated. Mating compatibility was evaluated in field cages under semi-natural conditions. The Argentinean population was obtained from a colony of the laboratory of the Instituto de Genética “E. A. Favret” (INTA Castelar), Buenos Aires, established in 2007. The Uruguayan population came from infested fruits of Acca sellowiana (Berg. 1855) Burret 1941 (Myrtaceae). At the moment of the trials, Argentinean flies were between 11 and 17 days old and Uruguayan flies were between 16 and 26 days old. Sexual compatibility was established using the index of sexual isolation (ISI), the male and female relative performance indices (MRPI, FRPI), and a Kruskal-Wallis one-way analysis of variance with subsequent pairwise comparison tests of the four types of pairs formed according to male and female origin. Latency, mating duration, and location of the couples were also recorded. The ISI value was significantly different from zero because 46of a greater performance of the Argentinean adults. There were no significant differences between the frequency of homotypic Uruguayan couples and heterotypic couples, whereas the frequency of Argentinean homotypic couples was significantly higher than the rest. No significant differences were found for the other evaluated parameters. Results suggest that Uruguayan populations belong to the Brazilian-1 morphotype considering that the greater performance of Argentinean flies is probably because of faster sexual maturation rates and an inherent greater mating propensity rather than to reproductive isolation.