Acquired von Willebrand disease is likely underdiagnosed due to the clinical variability in presentation and variety of conditions, including lymphoproliferative and myeloproliferative syndromes, autoimmunity, solid tumors, hypothyroidism, and cardiovascular disease, in which it can present. Pediatric patients with Wilms tumor have been reported in the literature with acquired von Willebrand disease and it has been theorized to occur in other pediatric solid tumors. Here we present the first reported case of acquired von Willebrand disease secondary to osteosarcoma in an adolescent patient, resolving spontaneously with treatment of her underlying disease.