ABSTRACT: BACKGROUND: Knowledge and awareness about childhood autism is low among health workers and the general community in Nigeria and other Sub-Saharan African countries. Poor knowledge and awareness about childhood autism, especially among health workers can compromise early recognition and interventions which had been known to improve prognosis in children with autism. In formulating policy and designing interventions for these children, there is need to develop a reliable tool that can be used in assessing baseline knowledge about childhood autism among health workers and the impact that future continued education and awareness campaign may have on such baseline knowledge. Knowledge about childhood autism among health workers (KCAHW) questionnaire was designed for this purpose. METHODS: The KCAHW questionnaire is a nineteen (19) item self-administered questionnaire that is divided into four domains. KCAHW questionnaires were distributed to fifty (50) psychiatric nurses involved in community mental health services in South-Eastern Nigeria to complete. After two weeks period, the KCAHW questionnaires were re-administered to the same fifty (50) psychiatric nurses to assess their knowledge about childhood autism and to assess the test-retest reliability and internal consistency of this questionnaire. RESULTS: KCAHW questionnaire showed good test-retest reliability when the mean domain and total scores at first and second time administration were compared. The four mean domain scores and the mean total scores at first and second time administration were significantly correlated. The questionnaire also had a good overall internal consistency when the mean scores of the four domains were correlated with mean total scores (Cronbach's alpha = 0.97). CONCLUSION: The KCAHW questionnaire is a reliable tool for assessing knowledge of health workers about childhood autism. It would be a useful tool in improving early recognition of features of autism among affected children in Sub-Saharan African and other developing countries of the world where knowledge and awareness about childhood autism is low.