The International Aicardi-Goutières Syndrome Association (IAGSA) was founded in 2000, its aim being to collect and analyse all available information on this rare syndrome (whose true incidence is not known) in order to increase knowledge of the pathology and the number of reported cases. We analysed the clinical, neuroradiological and biological characteristics of 21 new Aicardi-Goutières syndrome subjects (seven observed directly and 14 on whom we gathered detailed clinical information) and compared our findings with data in the literature. The main clinical symptoms (pyramidal and extrapyramidal symptoms, psychomotor delay, microcephaly) and neuroradiological features (basal ganglia calcification, atrophy, white matter alterations) observed show a greater homogeneity in our subjects than in the literature cases, which indicates an improvement in the diagnostic accuracy of Aicardi-Goutières syndrome. Other symptoms, such as feeding difficulties and irritability are less frequent, but characteristic and present early (even at onset of the disease). In the literature, doubts are expressed as to whether lymphocytosis and/or raised interferon-alpha in cerebrospinal fluid are crucial for a diagnosis of Aicardi-Goutières syndrome. Our data suggest that they are, and in particular that an important role is played by raised interferon-alpha. The clinical course seems to show different stages: early onset, rapid progression, severe deterioration, stabilization. Our follow-up seems to indicate a trend not necessarily towards a worsening, but instead towards a stabilization or even a slight improvement of the clinical picture.