Background <p>Delusional parasitosis is a rare, fixed, false belief that an individual is infested with parasites or other living organisms despite no laboratory evidence to confirm this belief. It can manifest as a shared belief, folie à deux, or by proxy.</p> Case presentation <p>This case report describes an 8-year-old patient with Trisomy 21 with delusional parasitosis by proxy. The patient’s mother remained fixated on the patient having a parasitic infection despite extensive reassuring evaluations. There were multiple normal-appearing pictures and videos of the patient’s urine, stool, skin and throat shown to the medical team, consistent with the “specimen sign” described in the literature.</p> Conclusions <p>Delusional parasitosis is rare and can be difficult to diagnose and treat. It has even more complexity and implications in pediatric or other vulnerable populations. A multidisciplinary treatment approach is important to build trust and prevent harm.</p>