The paper presents the optimum design of a Permanent Magnet Synchronous Generator for wind power applications. The proposed optimization strategy deals with two contradictory objectives: to reduce generator costs and to raise the energy yield. This task is accomplished by maximizing the difference between the energy proceeds and the generator costs. The generator operating cycle is taken into account by a Weibull function that represents the wind profile for a fictitious site. A thermal model is adopted to evaluate the winding temperature and prevent overheating. The optimally designed machine is a 3phase generator for 40 kW direct drive wind turbines. The results show that this strategy would produce a cost-effective machine.