There is significant amount of scientific literature regarding psychological variables that account as vulnerability/protective variables for the onset and maintenance of PTSD symptomatology. Among them, Big Five personality traits (openness, conscientiousness, extraversion, agreeableness and neuroticism). However, there is still little evidence regarding the underlying mechanisms that may explain that relationship. Transdiagnostic variables, such as intolerance of uncertainty or anxiety sensitivity, arise as potential candidates for being (at least partially) part of these mechanisms. Method. A sample of 300 participants from Spanish general population (Mage = 38.72; 54.7% women) completed an on-line survey in two separated moments: personality traits (NEO-FFI), intolerance of uncertainty (IUS-27) and anxiety sensitivity (ASI-3) at T1, and PTSD symptomatology (PCL-5) at T2, three months later. Results. Neuroticism (βstandarised = .144), intolerance of uncertainty (βstandarised = .195) and anxiety sensitivity (βstandarised = .269) at T1 predicted 25.5% of PTSD symptomatology at T2. Moreover, intolerance of uncertainty (a1a2 = .129) and anxiety sensitivity (b1b2 = .119) partially and complementary mediated the relationship between neuroticism at T1 and PTSD symptomatology at T2 (c' = .144). Discussion. This study is the first to analyse together, in a two-wave prospective study, the predictive capacity of personality traits, intolerance of uncertainty and anxiety sensitivity, over PTSD symptoms, and to test a mediation model that may help understanding the underlying mechanisms in the proved relationship between neuroticism and PTSD symptomatology. These results have significant implications for future development of targeted prevention and intervention programs aimed to traumatic events survivors.