Although combining corticosteroids and cyclophosphamide has greatly improved the prognoses of severe necrotizing vasculitides, some patients continue to have fulminating disease and die within the first year of diagnosis. To evaluate the characteristics of these patients, we retrospectively studied the files of 60 patients who died within the first year (20 patients with hepatitis B virus-associated polyarteritis nodosa [HBV-PAN], 18 with non-HBV PAN, 13 with microscopic polyangiitis [MPA], and 9 with Churg-Strauss syndrome [CSS]) and 535 first-year survivors (89 patients with HBV-PAN, 182 with non-HBV PAN, 140 with MPA, and 124 with CSS), 85 of whom died during a mean follow-up of 6.4 years. The 2 groups were compared for prognostic factors defined by the five-factor score (FFS) and Birmingham Vasculitis Activity Score at baseline, clinical signs, treatment, outcome, and causes of death. For first-year nonsurvivors, the clinical signs predictive of death were as follows: renal involvement (hazard ratio [HR], 1.6; 95% confidence intervals [CI], 1.09-2.3) or central nervous system involvement (HR, 2.3; 95% CI, 1.5-3.7), and a trend toward cardiomyopathy (HR, 1.4; 95% CI, 1.000-2.115). Older patients died earlier (HR, 1.04; 95% CI, 1.023-1.051). Gastrointestinal symptoms were most frequently associated with early death from HBV-PAN, while 83% of CSS patients died of cardiac involvement. Treatment had no significant impact on early death, except for patients with FFS > or = 2, for whom steroids alone were associated (p < 0.05). The major cause of early death was uncontrolled vasculitis (58%), followed by infection (26%). Cyclophosphamide-induced cytopenia and infection were responsible for 2 deaths. Despite these iatrogenic complications, early deaths were more frequently the consequence of insufficient or inappropriate therapy.