Computer-implemented method for the probabilistic assessment of fatigue of component parts in the presence of manufacturing defects, comprising at least a step of: a) importing predefined input data concerning at least one part of a component to be assessed and comprising: load case; finite-element static analysis data of said part; input parameters for analysis; parameters relating to the distribution of the defect; and parameters relating to the strength of the material; wherein said input parameters for analysis comprise at least one of the following: cycle ratio R=F min /F max, wherein F is the applied stress; fatigue life to be assessed; variability and distribution of material strength; variability and distribution of the applied stress; parameters for the description of the strength; number of units that are symmetrical to that assessed making up the model as a whole (N symm); characterized in that it comprises at least the following steps: b) distinguishing at least one surface region of said part from at least one internal region of said part, wherein said step (b) of distinguishing at least one surface region of said part from at least one internal region of said part comprises determining said surface region on the basis of a grid of said finite element analysis data and on the basis of said distribution of defects, and assessing said surface region as the volume comprised in a predefined distance from an external surface of said part; c) determining a volume and stress/deformation applied to said at least one surface region and to said at least one internal region; d) assigning said distribution of defects to at least one group of elements defined by a user; e) determining a maximum dimension of said defects in each surface or internal region (RE, RI) considered; f) determining a critical dimension of said defects in each surface region or internal region by considering the fatigue strength of the material at the number of cycles under consideration, said stress/deformation applied and the position of each surface or internal region (RE, RI); wherein the computer implemented method comprises performing said steps from c) to f) for all fatigue lives and for all loads applied under consideration; g) calculating the reliability for all the surface or internal regions considered. a) importing predefined input data concerning at least one part of a component to be assessed and comprising: load case; finite-element static analysis data of said part; input parameters for analysis; parameters relating to the distribution of the defect; and parameters relating to the strength of the material; wherein said input parameters for analysis comprise at least one of the following: cycle ratio R=F min /F max, wherein F is the applied stress; fatigue life to be assessed; variability and distribution of material strength; variability and distribution of the applied stress; parameters for the description of the strength; number of units that are symmetrical to that assessed making up the model as a whole (N symm); b) distinguishing at least one surface region of said part from at least one internal region of said part, wherein said step (b) of distinguishing at least one surface region of said part from at least one internal region of said part comprises determining said surface region on the basis of a grid of said finite element analysis data and on the basis of said distribution of defects, and assessing said surface region as the volume comprised in a predefined distance from an external surface of said part; c) determining a volume and stress/deformation applied to said at least one surface region and to said at least one internal region; d) assigning said distribution of defects to at least one group of elements defined by a user; e) determining a maximum dimension of said defects in each surface or internal region (RE, RI) considered; f) determining a critical dimension of said defects in each surface region or internal region by considering the fatigue strength of the material at the number of cycles under consideration, said stress/deformation applied and the position of each surface or internal region (RE, RI); wherein the computer implemented method comprises performing said steps from c) to f) for all fatigue lives and for all loads applied under consideration; g) calculating the reliability for all the surface or internal regions considered.