The literature currently available regarding PRS, which is generally in the form of case reports, suggests that the typical demographics are females displaying high achieving and perfectionist personality traits, with a mean age of 10.5 years. The diagnostic criteria are (i) clear food refusal and weight loss (ii) social withdrawal and school refusal (iii) partial or complete refusal in 2 or more of the following domains: mobilisation, speech, and attention to personal care (iv) active and angry resistance to acts of help and encouragement (v) no organic condition to account for the severity of the degree of symptoms (vi) no other psychiatric disorder that could better account for the symptoms. However, it does not feature in either ICD-10 or the more recent DSM-5. Since then, diagnostic criteria were established by Thompson and Nunn in 1997. Pervasive Refusal Syndrome (PRS) is a rare and little understood child psychiatric condition. We discuss the possible impact of ASD as a predisposing factor upon the progression and prognosis of PRS. We explore comorbidity and interaction of the two diagnoses. Although this differential has briefly been considered one in previous case, there have been no reported cases of PRS with a prior diagnosis of ASD. We discuss the symptoms present in this case and the differential diagnosis of ASD in PRS. He was admitted to a specialist Child and Adolescent Mental Health Unit. Other prominent symptoms included total mutism, school refusal, and self-neglect. We describe a case of PRS in a 9-year-old boy with a diagnosis of Autism Spectrum Disorder (ASD) presenting with severe weight loss due to extreme restriction of food and fluids. Pervasive Refusal Syndrome (PRS) is a rare child psychiatric condition.