This paper focuses on the study of the plastic zone in fatigue crack closure based on the results obtained by means of 3D Finite Element Analysis (FEA). These results show the crack behavior through the thickness. The plastic zone is visualized and quantified. It does not correspond to the classical shape. The plastic zone in the interior surface is similar to those obtained in 2D plane strain conditions and a reduced effect of closure is observed. However, close to the external surface, 2D plane stress results are not reproduced, the plastic zone size is smaller and an important change is observed. This transition is developed in a thin external portion of the specimen and it can only be captured if a fine mesh of the thickness is done.