This study analyzed eating disorder (ED) etiological factors for 100 midlife women ED inpatients, grouped by ED onset age: < 40 and > or = 40 years. Interpretative Phenomenological Analysis classified ED etiological influences into background contributors, immediate triggers, or sustainers. Family-of-origin issues, predominantly parental maltreatment, emerged as important background contributors, but not immediate ED triggers, regardless of onset age. Body image issues were also major background contributors regardless of onset age and further served as immediate ED triggers for many of the younger-onset patients, but not the older-onset patients. Family-of-choice and health issues were unimportant for younger-onset patients but were important ED contributors and triggers for older-onset patients. Emergent etiological differences suggest differential assessment and treatment needs for midlife ED patients based on ED onset age.