The inspection of damages detected in some blades of 300kW wind turbines revealed that the nature of these damages was probably due to a fatigue mechanism. The causes that had originated the failure (superficial cracks, geometric concentrator, abrupt change of thickness) have been studied, verifying, by means of the simplified evaluation procedure of fatigue life of the "Germanischer Lloyd" (GL) standard, that these causes can explain the failure detected in the period of time in which it happened. A suitable configuration for the repair of the damaged blades has been studied, by means of a finite element model. The proposed modifications repair the cracks and in addition contribute to relaxing the stress state in the affected zone. The introduction of a triangular reinforcement, which smoothes the re-entrant corner existing in the original design, incorporating a laminate of reinforcement, produces a significant decrease in the stress level in the damaged zone of the blades. (C) 2008 Elsevier Ltd. All rights reserved.