Sour cherry (P. cerasus) selections can be either self-compatible (SC) or self-incompatible (SI). As commercial cultivars must be SC to avoid the need for planting a pollinator, breeding for SC sour cherry cultivars is a high priority. The determination of whether a sour cherry cultivar is SI or SC is genetically controlled by the S-locus, a compound locus consisting of the stylar S-RNase and the pollen S, an F-box protein. Knowledge of the S-genotype of a sour cherry selection can be used to predict whether a selection is SI or SC. As previous research determined that any selection having a minimum of two non-functional S-haplotypes will be SC; S-genotyping is used in the Michigan State University (MSU) sour cherry breeding program to determine whether new selections are either SI or SC. Herein we detail the DNA diagnostic strategy used to determine S-genotypes of sour cherry and report the S-genotypes of four cultivars whose S-genotypes have not previously been reported.