Although it is recognised that autism spectrum disorder (ASD) and personality disorders (PDs) have a variety of factors in common, the exact nature of the relationship between ASD and the PDs remains unclear. The overlapping symptom profiles and complexities in developmental trajectories in ASD and PDs can lead to diagnostic uncertainty and to challenges in determining differential diagnoses. Features of ASD and PD can be misattributed and easily lead to misdiagnosis or missed diagnoses in patients who have a diagnosis of ASD, which may impact therapeutic pathways. Since differentiating between ASD and PD is such a complex task with implications for therapeutic approaches, it has been argued that there is a need for additional understanding and markers for facilitating diagnostic procedures. There is an urgent need to explore how clinicians make diagnostic decisions and the challenges they face in forming diagnostic conclusions. Where overlaps exist, it is important to consider how clinicians interpret and attribute certain characteristics within the context of ASD and/or PD diagnoses.