17-year-old and 14-year-old brothers were referred for evaluation of the cystic lesions on the mandibular anterior area with no symptoms. Neither their mother nor the brothers could recall any past trauma to those areas. Panoramic and intraoral radiographs revealed moderately defined cystic lesions on their mandibular anterior areas. Biopsies on both lesions revealed simple bone cysts. Hereditary cause or familial history of simple bone cysts could not be found in literature review. This case may have been a coincidence. However, further investigation is needed to find the cause of simple bone cysts occurring in patients those are closely related.