Between 1980 and 1995, 14 patients underwent treatment at Royal Prince Alfred Hospital for giant posterior circulation aneurysms. Two (14%) patients presented with subarachnoid haemorrhage (SAH). Eight (57%) of the 14 giant aneurysms were located at the basilar caput. A total of 7 (50%) contained significant intraluminal thrombus. Surgery was undertaken in 10 (72%) patients and endovascular embolization in the remaining 4 (28%). Of the patients treated surgically, 3 underwent clipping and a further 4 underwent Hunterian ligation. Of the 4 patients in whom embolization was carried out, 2 were coil treated and 2 balloon treated. Six (60%) patients undergoing surgery experienced significant complications, but in only 4 (40%) surgically treated patients was the complication directly attributable to the surgical procedure. All 4 (100%) patients treated interventionally suffered major complications, and in 3 (75%) of these the complication was directly attributable to the endovascular procedure. The clinical outcome at a median of 12 months follow-up was favourable in 8 (62%) of the 13 patients for whom follow-up information was available. We conclude that radiological techniques are not satisfactory for direct treatment of giant posterior circulation aneurysms and surgical exploration is advisable. In addition, timely referral to, and well planned management at, an experienced centre will undoubtedly contribute significantly towards securing a more favourable overall outcome.