In trout farming males exhibits lower growth rate and precocious sexual maturation in contrast to females. Since these traits are detrimental for intensive production, all females populations are most appreciated by fish farmers. Molecular markers sex-specific have been developed for rainbow trout that can be useful to diagnose the phenotypic sex of individuals. We evaluated the use of two SCAR markers (OmyP9 & Omy163), which show polymorphisms between males and females in rainbow trout as a diagnostic test for sexing farmed trout. Adult trout (n = 131) were genotyped to assess the association of the SCAR markers with phenotypic sex. To evaluate the correct performance of the SCAR marker in sex diagnosis, each marker and both were analyzed to estimate its specificity (the proportion of males that are correctly identified), sensitivity (the proportion of females that are correctly identified) and predictive value (the probability of the correct positive or negative female identification). Significant associations with phenotypic sex of both SCAR markers with sex were found. The sensitivity and predictive (positive and negative) indexes show higher values when both SCAR markers were considered (95.7, 77.4 and 94.4%, respectively). For joined SCAR markers a likelihood ratio (LR+) of 3.43 was obtained indicating its utility to establish a diagnostic test for sexing trout by use of marker-based analysis.