Endometriosis is influenced by both genetic and environmental factors. Genetic factors make up about half of the variation in endometriosis. Nevertheless, the genetics of endometriosis remains complex and in part unsolved, but recently, based on the results of few genome-wide association studies, some genetic susceptibility loci have been identified as associated robustly with the disease, providing new insights into potential pathways leading to endometriosis. Here, we present the case of a familial cluster composed by 3 sisters and their mother, all affected by endometriosis. Very severe gynecological and obstetric complications caused by the invasiveness of the disease have been observed in all members of the single family. The entire family has been genotyped for 3 single-nucleotide polymorphisms identified as associated with endometriosis. All the family members were homozygotes for the risk allele G for the rs1333049 variant in the <i>CDKN2BAS</i> locus. The genotype-phenotype association is just at the beginning of endometriosis research promising to face novel concepts for disease diagnosis and treatment.