A 5-year-old boy adopted from an overseas orphanage at age 3 presents with indiscriminate friendliness toward strangers, inability to seek comfort from his adoptive parents when distressed, and lack of social reciprocity with peers. His adoptive parents report that despite two years of consistent, loving caregiving, he shows no preferential attachment. The PMHNP diagnosing disinhibited social engagement disorder considers the neurobiological underpinnings of impaired attachment.