Arteriovenous malformations (AVM's) of lateral and sigmoid sinuses are acquired lesions evolving from a previously thrombosed dural sinus. Their natural history is usually that of gradual progression and hence surgery is frequently necessary. The preferred surgical treatment is complete excision coupled with packing of the sigmoid sinus. The operative approach is illustrated and discussed in detail. Results and complications are reviewed in 27 patients whose symptomatology had progressed under conservative management; 22 of these cases harbored primary lesions and five had recurrences. There were 22 excellent, one good, and two poor results (both of the latter from blindness that preceded surgery). There were two deaths, both in patients previously operated on with incomplete removal or obliteration of the AVM by attempted embolization.