The main goal of this research was to examine, using modern methods, the variability of phenotypic correlations of production performances and reproductive properties of Simmental cows reared on the farms of individual agricultural producers, in different breeding areas of the Republic of Serbia. The study of phenotypic correlations of milk performance and fertility properties in different regions of Serbia was carried out on a total of 3.056 primi parous Simmental heifers under control, with lactations completed within one year. The examined animals were reared on different individual farms, and mainly in very different conditions of housing and nutrition, depending on the breeding area. The study of phenotypic correlations included the following milk performance traits: milk yield, milk fat content, milk fat yield, yield of 4% corrected milk; and fertility properties: age at first calving and service period. The results of the study among other things indicate that although the phenotypic correlations between the fertility and milk performance properties show different degrees of variation, they should be taken into account in the final assessment of the breeding value of the animal, so that the breeding selection programs are more comprehensively designes.