The International Headache Society (IHS) classification system (1988) was developed primarily for headache disorders in adults and its validity for paediatric age is currently under discussion; in 1995 Seshia et al. proposed a revision of the criteria for migraine without aura to make diagnostic criteria more applicable to children. The purposes of the current study were to: (1) compare the IHS classification with the Seshia proposal, (2) compare the children affected by migraine without aura (MO) with the children affected by tension headache (TH) as defined by Seshia, for characteristics which are not included in the classification. The patients are a series of 320 children (mean age 9.9, SD 2.6 years; 144 males, 176 females) with recurrent or chronic headaches referred to a headache clinic in Milan, Italy. Using the Seshia criteria instead of the IHS criteria a higher number of children were included in the MO category: bilateral pain and family history of migraine were the most important factors which allowed a shift of children into this category. However, with the Seshia classification there was no reduction in the number of unclassifiable children. The reason why some children could not be classified was a short duration of attacks; the majority of unclassifiable children were 6 years old or less. No relevant difference was found between children with MO and children with TH for the following variables: occurrence of attacks in the afternoon or evening after school, reduction of attacks during school holidays, full-time schooling, after-school activities on school days, disordered daily life. On the contrary children with MO when compared with those with TH showed a higher number of precipitating factors and for the following factors a significant difference was found: exposure to TV or a computer, sleep deficiency, and strong emotions. Furthermore, children with MO showed a greater severity of attacks.