This paper examines the psychometric properties (reliability and factor structure) and validity (relationship with various self-report measures and SPEM dysfunction) of the SSQ or Schizotypic Syndrome Questionnaire, a 108-item inventory for the measurement of 12 prodromal or schizotypic symptoms present in Van Kampen's model of schizophrenic prodromal unfolding. This paper also provides normative data for the SSQ. The SSQ demonstrates adequate reliability and breaks down into three correlated factors: negative schizotypy, asocial schizotypy and positive schizotypy. Results further attest the construct validity of the instrument. Because of the implications of the SSQ model for the definition of schizophrenia, the instrument's three-dimensional factor structure and the nature of one of the factors are discussed in more detail. © 2006 Elsevier B.V. All rights reserved.