BACKGROUND The aim is to examine, in first episodes of schizophrenia, the appropriateness of the simple two-dimensional model of schizophrenia ('negative' and 'positive' dimensions) and more complex variants.

METHOD All patients with a first episode of schizophrenia who, over a two-year period, made contact with any of the public mental health services of the autonomous region of Cantabria in northern Spain were investigated. The psychiatric evaluation included, among other instruments, the Present State Examination (PSE-9), and the scales for the assessment of the 'positive' and 'negative' symptoms of schizophrenia (SAPS and SANS respectively). The dimensionality of the SAPS/SANS item scores and sub-scales was examined throughout the use of principal component analysis.

RESULTS The principal component solution that best fits the data obtained with the initial SANS/SAPS sub-scales reflects the existence of three different ('negative', 'positive', 'disorganisation') factors. The strategy adopted of repeating the analysis after extracting the principal components of the original sub-scales, revealed that although the nature and item composition of the initial 'negative' and 'disorganisation' factors were in general confirmed, the 'positive' dimension presented a more complex structure with at least two 'positive' ('Non-Paranoid' and 'Paranoid') independent factors.

CONCLUSION The psychopathological structure of the early stages of schizophrenia, as evaluated by the SANS/SAPS, is characterised by the presence of four dimensions: two 'positive', one 'negative' and one 'disorganisation'.