The Kitagawa-Takahashi (KT) diagram [1] represents a boundary in terms of crack size and stress range for which infinite fatigue lifetime of structural or mechanical components can be safely ensured due to non-propagating micro-and macrocracks [2]. The fatigue life assessment can be related to the classical fatigue limit concept, based on experimental S-N curves, and the threshold stress intensity factor range or threshold value of the cyclic J-integral, based on fracture mechanics using propagation laws. In this paper, a procedure is proposed to obtain the probabilistic Kitagawa-Takahashi diagram for structural components. This procedure is based on the equivalent initial flaw size (EIFS) model [3-4] and is supported by the probabilistic S-N model proposed by Castillo and Fernández-Canteli [5]. With the EIFS concept and based on fracture mechanics, particularly on elastoplastic cyclic J-integral, the initial defects of the structural components will be taken into account. This approach, combined with the probabilistic S-N field, allows the generation of the probabilistic distribution of the EIFS. Also, a probabilistic KT diagram (P-KT) is presented as an alternative way to understand the distribution of the EIFS. The procedure proposed is applied to a notched plate made of P355NL1 steel. The performances of predictions are analyzed and deviations discussed. References [1] Kitagawa H., Takahashi S. Applicability of fracture mechanics to very small cracks or cracks in the early stage.