Background Posttraumatic stress disorder (PTSD) attributed to non-disaster events has increasingly gained attention but only few study of PTSD was based on community-based samples. PTSD in the underlying community is poorly understood regarding the incidence, prevalence, time trend, seasonal variation, and past history of outcome. It is also unclear whether other putative factors are responsible for incident PTSD cases after controlling for time series factors. Objectives Annual and age-and gender-specific incidence and prevalence of PTSD were estimated and compared. Bayesian time series model was used to model seasonal variation, time trend and autoregressive order together with demographic factors and other putative factors. Method We used a five-year longitudinal follow-up retrospective cohort spawned from a community-based integrated screening program to identify incident PTSD cases. The autoregressive order was determined and Bayesian Poisson Autoregressive Time Series Model was applied to modeling time trend, seasonal variation, and autoregressive order (past history of PTSD) by using Bayesian Monte Carlo Markov Chain simulation method. We used two different approaches, including dummy variable and trigonometric function, to model the seasonal variation of PTSD. Statistical significance of time series component was assessed by a series of nested models using DIC criteria and mean squared predictive error. Risk factors accounting for incidence of PTSD were analyzed with univariate and multivariate models. Results The annual incidence of PTSD was 0.08%, which is 10 times of the prevalence rate at baseline year (1999). Considering second order autocorrelation in the time series model, seasonal variation and time trend were statistically significant. For demographic characteristics, age, marital status, and education level were highly associated with incidence of PTSD. Significant risk factors included cardiovascular heart disease (adjusted relative risk (RR)=1.39,95% confidence interval (CI): 1.03-1.85), major depression (adjusted RR=2.67,95% CI: 1.70-4.14) and dysthymia (adjusted RR=7.52, 95% CI: 5.49-10.17). Conclusions Prevalence and incidence rate of PTSD was estimated on the basis of a community-based cohort data. Bayesian time-series model was applied to ascertaining significant time trend, seasonal variation, and autoregressive order of PTSD. This model is also useful for identifying individual attributes related to PTSD, such as age, marital status, education, cardiovascular heart disease, major depression and dysthymia.