Clinical features of green pit viper bites vary from asymptomatic to fatal bleeding. Antivenin promptly reverses the coagulopathy but has considerable adverse side effects. In this study, potential clinical predictors of severe outcomes (wound necrosis, wound infection, and systemic bleeding) and antivenin allergy were determined in 271 moderate to severe cases of green pit viper bites by multivariate analysis. The incidences of systemic bleeding, wound necrosis, secondary infection, and antivenin allergy were 17.3%, 6.6%, 5.5%, and 20.8% respectively. The predictors of systemic bleeding were the combination of thrombocytopenia and prolonged venous clotting time and bite sites away from digits. A bite on the fingers or toes was a risk factor for skin necrosis (P = 0.03). Systemic absorption of the venom from digits may be poor, resulting in severe local but mild systemic effects. The presence of blisters often led to necrosis and secondary infections (P = 0.0037 and P = 0.0006, respectively). Although negative skin test results do not exclude the possibility of antivenin allergy, positive results indicate a high risk (P = 0.016) requiring special precautions.