Von Willebrand disease (VWD) is one of the most common congenital blood clotting diseases. It is mostly inherited in an autosomal manner, which means it affects both sexes equally. Rarely and in the more severe forms of the disease, it can be passed on in a recessive manner. The diagnosis of VWD is complex. Detailed medical anamnesis and patients' histories follow, along with basic and specific laboratory tests for determining VWD. Activity of VWF is possible to measure using different types of tests. The method which is currently used in the Specialized Hematology Laboratory of the Clinical Department of Hematology of the University Medical Center in Ljubljana (SHL KOH UKCL) is based on a standard ristocetin cofactor assay (RCo) measured by platelet aggregation and is particularly time consuming. The aim of this master's thesis was to introduce a new automated version of the ristocetin cofactor assay (VWF:GP1bR) into the laboratory. Existing samples of patients (N = 50) were analysed and we then compared the results found to those previously determined using the current RCo method. Clinically, the method is particularly important in patients with reduced VWF activity and the diagnosis is more difficult; therefore, we made a separate analysis for these samples. Based on a statistically processed data, we concluded that the new method VWF:GP1bR is acceptable for transfer to daily clinical practice, as the pre-defined clinical and analytical endpoints are met (within and between series imprecision for normal VWF activity (CV < 5,5 %) and for low VWF activity (CV < 7 %)). In contrast to the former RCo method by aggregometer, the new method VWF:GP1bR is automated; with it, a reliable result is achieved much faster and it is more accurate and less costly. At the same time, the methods strongly correlate and match. The new method VWF:GP1bR also corresponds to the results found using the method VWF:GP1b / VWF:Ab which is also used for measuring VWF activity in the laboratory: SHL KOH UKCL.