OBJECTIVES: To determine the balance between risks and benefits of aneurysm occlusion in elderly patients with subarachnoid haemorrhage (SAH), as function of patient characteristics and aneurysm characteristics. The analysis focused mainly on the effects of patient age, clinical condition and day of admission after SAH. METHODS: With Markov model Monte Carlo simulation we evaluated health gains, in quality-adjusted life years (QALY), additional costs, and incremental cost-effectiveness ratios (ICER) of aneurysm occlusion in 192 subgroups of patients. Subgroups were defined by age (70-74, 75-79, 80-84, 85+ years), neurological condition at admission (poor or good), day of admission after SAH (<4, 4-10, 11-21 days), gender, aneurysm size (<10 mm or  ≥10 mm) and aneurysm location (anterior or posterior circulation). RESULTS: In patients admitted in poor condition ≥10 days after SAH, and patients older than 80 years, admitted in poor condition ≥4 days after SAH, aneurysm occlusion implied QALY loss as well as increased costs, regardless of aneurysm size and location. The ICER of occlusion was better than € 50,000/QALY only in women aged 70-79 years, and men aged 70-74 years, admitted in good condition in <4 days. Occlusion was both beneficial and cost-saving in women aged 70-74 years, admitted in good condition in <4 days, with a small posterior aneurysm. CONCLUSIONS: Occlusion of ruptured intracranial aneurysms instead of conservative treatment improves outcome in some elderly patients, but not in all, and will often incur unacceptably high costs. The occlusion benefits of reduced risks of rebleeding and recurrent SAH only ensure the final balance is positive when patients can profit from them, in fair health, over several years. Thus, beyond some patient age, occlusion should no longer be viewed as standard treatment, but as option, viable only in patients with a prolonged life expectancy.  Supported by the Netherlands Heart Foundation (grant #2006B082).