Our aims were to investigate the frequency of intracranial lesions detected by cranial computed tomography ( CT-scan) amongst adult patients who had clinical warning criteria (CWC) for secondary neurological headaches and to determine the importance of CWC in predicting a possible lesion on CT-scan. Seventy consecutive patients with headache exhibiting CWC were included in this prospective study. The CWC included: (i) increase in the intensity and frequency of headache; (ii) abrupt onset of headache; (iii) persistence of headache despite analgesics; (iv) alteration of the characteristics of headache; and ( v) presence of focal neurological symptoms or findings. The mean age of the patients was 46.5 years; the female-to-male ratio was 1.5. Of the patients, 35.7% had a neurological cause identified by CT-scan, and 64.3% had normal CT-scan. In the patients without lesion, of headaches, 64.4% were primary, and 35.6% were from undefined headache group. Although, of the above criteria, only the 5(th) was different markedly in the patients with lesion than the patients without lesion, in evaluation by CT-scan the secondary neurological headaches in adults, all CWC should look for absolutely in their history and physical examination.