The objective of this study was to investigate whether clinical and laboratory data, Birmingham vasculitis activity score (BVAS) and five factor scores (FFS) at diagnosis could predict relapse in 30 patients with polyarteritis nodosa (PAN) having the follow-up duration for over 12 months. We reviewed the medical charts of 30 patients with PAN. We obtained clinical and laboratory data at diagnosis, and we compared them between the two groups based on relapse. The optimal cut-off values of BVAS and FFS (1996) at diagnosis to predict relapse were extrapolated. The mean age of patients (15 men) was 50.8 years, and the mean follow-up duration was 64.1 months. Nine patients (30.0%) had experience relapse after remission. Patients having relapse showed the higher frequency of weight loss and ocular symptoms and the less frequency of diastolic hypertension than those having not (p < 0.005 for all). On multivariate logistic regression analysis, weight loss was the only independent predictor of relapse, but on Cox Hazard model analysis, its statistical significance disappeared. The mean initial BVAS and FFS (1996) of patients in relapse group were higher than those of patients in no relapse group (p < 0.005 for all). Patients having initial BVAS over 13.5 and FFS (1996) over 1 exhibited significantly higher risk of relapse than those having not (RR 40.0 and RR 7.0, respectively). However, initial BVAS over 13.5 only remained significant in Kaplan-Meier survival analysis. In conclusion, BVAS over 13.5 at diagnosis was the only independent predictor of relapse of PAN.