The present study is part of a survey of subarachnoid hemorrhage cases observed in 16 neurosurgical and 8 neurological departments in Italy between June 1985 and June 1986. Warning signs preceding major hemorrhage were analyzed in 364 patients with intracranial aneurysms confirmed by angiography and reliable clinical history. Seventy-four (20.3%) had warning signs. Clinical features of premonitory warning signs were compared with symptoms of 78 patients without a history of minor leak and clinical grade 1 (according to the criteria of Hunt & Hess) at admission. Symptoms of warning signs are generally clear enough to be considered a misdiagnosis of intracranial aneurysm. Thunderclap headache described as severe, unusual and sudden was the main symptom in every case though the higher frequency of focal of diffuse signs in groups with a correct diagnosis attracted more careful attention in referral and diagnostic-therapeutic management. Improving the identification of minor leak and defining diagnostic strategy are discussed.