Rothmund–Thomson syndrome (RTS) is a rare autosomal recessive disorder of which approximately 300 cases have been reported in the literature. Patients with RTS often present early in life with skeletal and dental abnormalities, short stature, juvenile cataracts, and a characteristic poikilodermal rash. They are at increased risk for the development of osteosarcoma that usually presents by the second decade of life. The genetic defects underlying RTS are truncating mutations in RECQL4, a gene involved with chromosomal stability. Several cases of primary hematological malignancies have been reported in RTS, but it is unclear whether patients with RTS are at higher risk to develop either primary or secondary hematological malignancies. We report a patient with RTS who presented to our clinic at the age of 7, subsequently developed multifocal and recurrent osteosarcoma that was followed by the development of a myelodysplastic syndrome with subsequent progression to acute myeloid leukemia.