The circulation distribution over a blade of a wind turbine model is estimated by use of a vortex model, which is matched with measured wake properties. With near wake velocities and the Biot-Savart law an optimization scheme is constructed to estimate the circulation distribution over the blade using a polynomial function series to approximate the circulation distribution. The velocities resulting from the calculated distribution are compared with the measured data, and deviations are discussed and explained. The vortex model offers insight into how the measured velocities can be separated into induced velocities of the different parts of the vortex system, such as the influence of the tip vortex. The sensitivity of the vortex model to its most uncertain parameters is tested. Finally the circulation distribution obtained with the vortex model is compared with the circulation distribution obtained through application of a blade element momentum (BEM) code. The BEM results show an underestimation of the circulation near the root and an overestimation of the circulation near the tip with respect to the vortex model results. Copyright © 2004 John Wiley & Sons, Ltd.