Objective: There are two theories (by Horowitz and by Foa) which attempt at explaining the process of posttraumatic stress disorder (PTSD) development by information dissonance. The purpose of the present study was to verify these theories via cross-sectional and longitudinal studies. Materials and Methods: The study based on a cross-sectional design was performed on a representative group of Polish firefighters. The study using a longitudinal protocol was conducted among police officers. The level of PTSD was assessed using the Questionnaire for PTSD Measurement (K-PTSD). The sense of coherence (SOC) was measured with the Polish adaptation of the Orientation to Life Questionnaire by A. Antonovsky. Results: In the cross-sectional study, the correlation coefficients between K-PTSD and SOC were –0.35 (p < 0.001) in the group of firefighters and –0.47 (p < 0.001) in that of police officers. In the longitudinal study, the relationship between SOC and PTSD symptoms appeared to be curvilinear and had the U-letter shape. Therefore, we used ANOVA for statistical analysis. Unfortunately, the F(2.31) = 1.900 and p > 0.05 indicated that the tendency we observed was not statistically significant. Conclusions: We would like to propose two possible explanations for the difference in the relationships between SOC and PTSD symptoms obtained in the studies employing the cross-sectional and the longitudinal protocols.