Background: Anxiety Disorder (AD) is among the most common psychiatric comorbidity in children and adolescents with Autism Spectrum Disorder (ASD). Likewise, parental psychological distress (PPD) was linked to anxiety symptoms in children and adolescents with ASD. The aim of this study was to characterise, in a sample of children and adolescents with ASD, anxiety symptoms, the functional impairment associated and the presence of PPD. Methods: Participants were divided into three groups based on their diagnosis: children and adolescents with a diagnosis of ASD + AD, others with a diagnosis of AD but without a diagnosis of ASD, and others with a diagnosis of ASD but without a diagnosis of AD. Results: Group ASD + AD showed lower global functioning than Group ASD and Group AD. Generalised Anxiety Disorder, Separation Anxiety Disorder and Specific Phobias were more frequent in Group ASD + AD. Our findings also showed higher depressive symptoms in Group ASD + AD, both in the child and parent reports. Finally, parents of the Group ASD + AD revealed higher levels of PPD. Conclusions: Our findings suggest that early assessment of AD with functional impairment associated with the role of PPD could define individualised treatments and nsequently mean a better prognosis in children and adolescents with ASD and AD.