Assessment for Autism Spectrum Disorders (ASDs) is essential to provide comprehensive understanding of child functioning, advise diagnosis, and inform treatment. Evidence-based guidelines for ASD diagnosis have been developed; however, results from studies conducted outside Canada suggest disparities between these guidelines and clinical procedures. The objectives of this study were to: (a) understand Canadian clinicians’ practices in assessment of ASDs; (b) compare assessment practices to evidence-based guidelines; and (c) identify challenges. Eighty-six Canadian clinicians participated in a survey. Findings suggested a disparity between reported practice and evidence-based guidelines in terms of processes implemented and use of consultation practices. Clinicians indicated that organizing assessment teams and identifying ASDs in high-functioning children are challenges. Overall, this study provides a picture of the current Canadian context for ASD diagnosis. This information may inform the development of additional guidelines and training opportunities, and highlight policy changes required to alleviate challenges in the diagnostic process.