We evaluate clinical characteristics of headache in a group of subjects > 12 years to assess the sensitivity and specificity of the IHS criteria. We consider whether age at onset may influence the clinical features. We used a semi-structured questionnaire to examine 136 patients consecutively referred to our division. We considered the following subdiagnoses: IHS 1.1, 1.2, 1.7, 2.1, 2.2, 2.3. Migrainous disorders were found to be more common than non-migrainous headaches. A definite diagnosis was established in 68.1% of the migrainous group and in 86.6% of the tension-type headache group. Unilateral location, severe intensity of pain, the presence of nausea, vomiting, phonophobia and photophobia were features which differed between migrainous and non-migrainous subjects. No difference was found regarding aggravation of the headache by physical activity. On the basis of the criterion duration of attacks < 2 hours, IHS 1.7 was found to differ significantly from other migraine types. With the exception of the presence of vomiting in migrainous patients, the age at onset was not found to be a factor influencing the characteristics of the headache. Diagnostic criteria for migraine were highly specific but poorly sensitive, and those for tension-type headaches highly sensitive but less specific. The sensitivity/specificity of the IHS criteria in adolescent migraine can be influenced by the heterogeneity of the clinical characteristics. In fact, the intensity, the location and the quality of pain were similar to those found in childhood migraine, while the concomitant symptoms were less frequent than in childhood and in adult migraine. Further studies are needed to define the degree of severity of the clinical features in adolescent headache and to address the question of the validity of the IHS criteria.