A von Willebrand syndrome was present in four patients with sickle cell trait and hematuria. The first two patients had severe anemia and active bleeding and received cryoprecipitate, with prompt cessation of hemorrhage. All of the patients had repetitive laboratory and clinical features; that is, reduced, but detectable, factor VIII-related antigen, heterogeneity of, and incongruities within, the coagulation studies performed but consistently defective platelet aggregation to ristocetin, correctable only with normal plasma. Bleeding outside the genitourinary tract never was observed. Because of the focal nature of the hemorrhage, the hematuria may not have been perceived as part of a general hemorrhagic disorder and the diagnosis not pursued. These observations suggest that when sickle cell trait and hematuria occur together, a von Willebrand syndrome should be a major diagnostic consideration that ultimately may point toward a rational, effective, easily administered, and clincially acceptable form of treatment with cryoprecipitate.