The familial occurrence of childhood cancers has been proven for a long time. Wilms’ tumors often do not have a clear germline genetic cause. However, approximately 2% of all nephroblastoma cases are familial. Descriptions of twins with the same cancer are extremely rare, so our aim was to present the background of the available literature of the occurrence of Wilms’ tumor in a pair of monozygotic twin girls with detailed clinical, histological, and molecular analysis. Two twins were born of unrelated Caucasian parents. Family history revealed no known chronic diseases or malformations. At the age of 3.5 years, the first twin was admitted to the emergency department due to hematuria and abdominal pain. Ultrasound examination revealed an enlarged right kidney, 12.8 cm, with a mass in the upper pole measuring 56 × 69 × 78 mm. The second girl was referred for an abdominal ultrasound, which revealed a right kidney measuring 8.6 cm with a central mass measuring 54 × 45 × 41 mm. Both children underwent surgical resection, and the histopathological result showed a mixed form of nephroblastoma, predominantly epithelioid with residual blastemal compartment. Detailed clinical, histological, cytogenetic, and molecular analyses were performed on both sisters. It was also decided to identify environmental factors. Information was obtained that the girls’ parents run a farm and regularly use pesticides and chemical rodenticides. Based on our observations and the available literature, Wilms tumor in monozygotic twins may be present. Both genetic and environmental factors may be involved in the development of tumors. After excluding methylation abnormalities and mutations in the genes studied, we questioned whether the onset of Wilms tumor in both sisters could be the result of exposure of the twins’ parents to pesticides.