Abstract: The present invention is based on the finding that administration of polypeptides comprising two immunoglobulin single variable domains (ISVD) against von Willebrand Factor (vWF) to human patients with an initial episode of thrombotic thrombocytopenic purpura (TTP) episode results in improved outcomes, including a faster time to platelet count response lower proportion of patients with either death, recurrence or a major thromboembolic event (TE) during the treatment period, lower recurrence rate, and prevention of refractoriness. The invention provides a polypeptide comprising two ISVD against vWF for use in treating a vWF-related disease, preferably TTP, in a human in need thereof. The invention further relates to dosage unit forms, kits and medical uses for treating TTP.