OBJECTIVES. To assess efficacy and safety of two equine F(ab')2 antivenoms currently used to treat envenoming by European vipers. DESIGN. Retrospective case review study. SETTING. Case records collected by the Swedish Poison Information Centre concerning patients treated in Swedish hospitals for bites by the common European adder, Vipera berus. SUBJECTS. Patients presenting with V. berus envenoming treated with antivenom (n = 30) and two groups of patients not given antivenom (n = 16 and n = 38). MAIN OUTCOME MEASURES. Clinical course and time in hospital were retrospectively studied and compared in patients treated or not treated with antivenom. RESULTS. There was a significantly lower incidence of extensive oedema (23 vs. 88%) and anaemia (10 vs. 50%) in the antivenom-treated group, and the hospital stay was shorter (median: 3 vs. 6 days). Antivenom treatment also resulted in prompt clinical improvement in the acute phase. Adverse effects consisting of urticaria and serum sickness occurred in 10% of the patients given antivenom. CONCLUSIONS. Antivenom treatment was associated with a reduced morbidity in severe V. berus envenoming. However, the occurrence of allergic side-effects is not negligible with this type of antivenom.