Valid and reliable tools to measure mental health are a key requirement to developing a robust evidence base on mental health difficulties and autism. There are several reasons why mental health measures developed for the neurotypical population may not be valid and reliable when used with autistic adults. Using data collected from a national evaluation of community-based, specialist autism provision in England, this study assessed the psychometric properties of the General Health Questionnaire (GHQ-12) in a population of autistic adults without learning difficulties. We examined the measure's acceptability, reliability and internal construct validity. The GHQ-12 was found to have good psychometric properties in this population. This provides first evidence that this measure can be used with autistic adults without LD.