Introduction: Diagnosis, treatment monitoring and assessment of desmopressin effect in haemophilia A patients are performed by measurement of factor VIII activity (FVIII). The two assays commonly applied are the one-stage assay and the chromogenic assay. Especially in non-severe haemophilia A, discrepancies between these assays are common. It is still unestablished which assay corresponds best with bleeding phenotype and desmopressin effect. Aim: To correlate FVIII levels measured by the one-stage assay and by the chromogenic assay with bleeding phenotype and, additionally, to compare FVIII assay discrepancies before and after desmopressin administration. Method: Factor VIII was measured in 130 non-severe haemophilia A patients during routine visits to the outpatient clinic and/or during desmopressin testing. FVIII was measured by both the one-stage assay and the chromogenic assay. Discrepancies between assays were defined as at least a twofold difference of FVIII or an absolute FVIII difference between measurements of ≥0.10 IU/mL. Bleeding phenotype was defined as annual number of treated bleedings (adjusted ABR). Results: Hundred and thirty non-severe haemophilia A patients were included. In 31/130 patients, assay results were discrepant. However, FVIII measurements with both assays correlated adequately with adjusted ABR. In addition, in 27/130 patients FVIII measurements at baseline and after desmopressin administration were analysed. In 13/27 patients, all measurements were either equivalent or discrepant when results were compared. In 14/27 patients, this was not the case as both equivalent measurements and discrepant measurements at different time points within one patient were observed. Conclusion: Neither the one-stage assay nor the chromogenic assay is superior in predicting bleeding phenotype. In addition, equivalent or discrepant FVIII results measured before desmopressin do not always predict FVIII assay results after desmopressin administration. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.