The 10-item Autism-Spectrum Quotient (AQ10) is a self-report questionnaire used in clinical and research settings as a diagnostic screening tool for autism in adults. The AQ10 is also increasingly being used to quantify trait autism along a unitary dimension and correlated against performance on other psychological/medical tasks. However, its psychometric properties have yet to be examined when used in this way. By analysing AQ10 data from a large non-clinical sample of adults (n = 6,595), we found that the AQ10 does not have a unifactorial factor structure, and instead appears to have several factors. The AQ10 also had poor internal reliability. Taken together, whilst the AQ10 has important clinical utility in screening for diagnosable autism, it may not be a psychometrically robust measure when administered in non-clinical samples from the general population. Therefore, we caution against its use as a measure of trait autism in future research.