The major causes of mortality and morbidity in patients surviving the rupture of a saccular aneurysm are subsequent bleeding and vasospasm. The purpose of this study was to evaluate the influence of early treatment of ruptured aneurysms with Guglielmi detachable coils on the incidence of subsequent bleeding. Thirteen patients were treated within 72 hours of initial aneurysm rupture with Guglielmi detachable coils. Excluding three patients who died 2, 4, and 12 weeks after initial hemorrhage, all others have been followed up for intervals between 6 and 36 months (mean, 16 mo). None of these have had either clinical or radiographic evidence of subsequent bleeding. Assuming that there is a 30% incidence of subsequent bleeding in conservatively (nonsurgically) treated patients, the 0% subsequent bleed rate observed in this subgroup was significant at a P value of 0.01. Only one procedure-related complication occurred in this series, and 9 of 13 (69%) aneurysms were 100% occluded at the time of initial treatment. All aneurysms were at least 90% occluded at the end of initial treatment. In addition to reducing the risk of subsequent bleeding, early treatment facilitated the institution of an aggressive approach for management of both vasospasm and increased intracranial pressure. Patient outcome, as measured by the Glasgow Outcome Scale, was good in 9 of 13 (69%), poor in 1 of 13 (8%), and death in 3 of 13 (23%) patients. The results of this study suggest that early Guglielmi detachable coil treatment of ruptured aneurysms may be effective in reducing the incidence of subsequent bleeding and can be performed with a low incidence of complications.(ABSTRACT TRUNCATED AT 250 WORDS)