Background: The combination of osteogenesis imperfecta (OI) and acute lymphoblastic leukemia (ALL) is uncommon, as evidenced in the world literature. Case report: We present the case of a pre - school patient with a family history and clinical and radiological characteristics compatible with OI, who is enrolled in ALL, receiving chemotherapy according to BFM 2009 protocol. In our case, from a clinical perspective, this underlying condition did not affect their ability to tolerate and respond to chemotherapy. Discussion: It is well described that genetic and chromosomal abnormalities increase the risk of leukemia, however the relationship between osteogenesis imperfecta and acute lymphoblastic leukemia is rare. In the world literature, there are few cases mentioning this association. It is important to continue observing the occurrence of later cases, which allow describing if there is a direct relationship between these two entities.