BACKGROUND: The risk of patients dying of pulmonary embolism (PE) or bleeding during the treatment of deep vein thrombosis (DVT), and whether these risks are influenced by patient age, has not been thoroughly studied. METHODS: We used data from the Registro Informatizado de la Enfermedad TromboEmbólica (RIETE) to assess the risk of fatal PE and fatal bleeding in 16,199 patients with lower limb DVT (without symptomatic PE at the time of inclusion) during the 3 months after diagnosis, with patients categorized according to age. RESULTS: During the 3 months of anticoagulant treatment, there were 31 fatal PEs (0.19%) and 83 fatal hemorrhages (0.51%). During the first 7 days of therapy, the frequency of fatal PEs was similar to that of fatal bleeding (12 vs 14 deaths, respectively; odds ratio [OR], 0.86; 95% confidence interval [CI], 0.39-1.87). However, from days 8 to 90, the frequency of fatal bleeding was greater than that of fatal PE (69 vs 19 deaths; OR, 3.64; 95% CI, 2.22-6.20). The higher frequency of fatal bleeding compared with fatal PE from days 8 to 90 appeared to be confined to patients who were aged ≥ 60 years. Multivariate analysis showed that patient age was independently associated with an increased risk of death from bleeding during the first 3 months: every 10 years the OR increased by 1.37 (95% CI, 1.12-1.67). CONCLUSIONS: During the first week of treatment, the risk of fatal bleeding and fatal PE were similar. Then, particularly in patients who were aged ≥ 60 years, the risk of dying from bleeding exceeded the risk of dying from PE.