Abstract: Angelman syndrome is a condition characterized by developmental delay due to abnormalities in the maternally derived chromosome 15q11-q13. Typical features include impaired expressive language, an ataxic gait, and seizures. Hyperactivity may result in accidental bruises and abrasions, raising issues of possible inflicted injury. A fascination with water may predispose to drowning. A 5-year-old boy with an established diagnosis of Angelman syndrome is reported who died of upper airway obstruction due to massively enlarged tonsils complicating infectious mononucleosis. Assessment of the severity of underlying illness in developmentally delayed children may be difficult due to failure to vocalize worsening symptoms and distress. In addition, signs of upper airway narrowing due to infection in Angelman syndrome may be masked by the sucking and swallowing difficulties that affected individuals may have with drooling and excessive chewing and mouthing behavior.