The validity of the Birmingham Vasculitis Activity Score (BVAS) as an index of disease activity and a predictor of the prognosis and outcome in patients with MPA has not yet been established in Japan. We conducted a retrospective study of the data of 73 patients with MPA who were followed up for at least 2 years. We divided the patients into two groups according to the BVAS, namely, the high-BVAS group (≥16) and the low-BVAS group (<16), and compared the clinical characteristics. In addition, the distribution of the BVAS items in the patients and the items contributing to the total score in MPA patients were analyzed. Remission was achieved in 85% of patients at 1 month. There were no significant differences in the serum CRP, creatinine (Cre), or MPO-ANCA between the high- and low-BVAS group; however, the survival time was significantly shorter (p = 0.048) and the mortality rate significantly higher in the high-BVAS group (p = 0.04). The items of the BVAS contributing to the total score were motor neuropathy, sensory neuropathy, pulmonary infiltrate, hematuria, proteinuria, Cre ≥5.6 mg/dL, hypertension, scleritis, rise in Cre by ≥30%, and myalgia. BVAS was found to be a useful tool for determining the disease activity and outcome in patients with MPA in Japan. The initial BVAS was also predictive of the mortality and survival time and can also be used as a prognostic tool; therefore, use of the tool may facilitate the selection of appropriate treatment.