Although treatment dropout is common among patients with eating disorders, very few studies have examined predictors of non-completion in day treatment. We investigated various potential predictors of dropout from adult day treatment. Participants were 295 adult patients with a diagnosis of Anorexia Nervosa (restricting or binge-eating/purging subtype), Bulimia Nervosa (BN), Other Specified Feeding or Eating Disorder, or Avoidant Restrictive Food Intake Disorder. Predictors included eating-disorder characteristics, motivation at the commencement of treatment, Body Mass Index (BMI), time spent in treatment and personality dimensions. Logistic regression analyses showed that for patients with a BMI of less than 20 at the start of treatment, low BMI was a significant predictor of staff-initiated termination due to not meeting weight gain goals. Furthermore, completing less than 6 weeks of treatment was associated with staff-initiated termination. For the whole sample, those with higher changes in weight over the course of treatment were less likely to terminate prematurely. None of the other predictor variables yielded significant results. Results of the current study highlight characteristics of patients who are more likely not to complete day treatment and can help identify patients who may be at risk for not succeeding in multi-diagnostic day treatment programs.