OBJECTIVE—The purpose of this study was to identify predictors of the onset of disturbed eating behavior (DEB) in adolescent girls with type 1 diabetes. RESEARCH DESIGN AND METHODS—In this prospective study, participants completed the Children's Eating Disorder Examination interview and self-report measures at baseline and at four follow-up assessments over 5 years. Participants were 126 girls with type 1 diabetes, aged 9–13 years at baseline. Of the 101 girls who did not have DEB at baseline, 45 developed DEB during the follow-up period; the 38 for whom data were available for the assessment before onset of DEB were compared with 38 age-matched girls who did not develop DEB. DEB was defined as dieting for weight control, binge eating, self-induced vomiting, or the use of diuretics, laxatives, insulin omission, or intense exercise for weight control. RESULTS—Logistic regression indicated that a model including BMI percentile, weight and shape concern, global and physical appearance-based self-worth, and depression was significantly associated with DEB onset (χ2 = 46.0, 5 d.f., P < 0.0001) and accounted for 48.2% of the variance. CONCLUSIONS—Even though scores on the measures were within the published normal range, the onset of DEB was predicted by higher depression and weight and shape concerns and lower global and physical appearance–based self-worth as well as higher BMI percentile 1–2 years earlier compared with those not developing DEB. Early interventions focused on helping girls with diabetes develop positive feelings about themselves, their weight and shape, and their physical appearance may have protective value.