The need exists to identify children with type 1 diabetes who are at risk for poor outcomes, and we hypothesized that missed appointments could be a useful indicator. We aimed to describe the frequency of missed medical appointments in children with type 1 diabetes and evaluate the relationship between missed appointments and poor disease control. Medical records of 1,002 children aged 0-17 years with type 1 diabetes and two or more scheduled appointments during a 43-month period were reviewed. Sixty-eight percent of patients missed no appointments, 17% missed one appointment, and 15% missed two or more appointments. Compared with patients who missed no appointments, patients who missed two or more appointments were three times more likely to have a diabetic ketoacidosis episode and three times more likely to have a hemoglobin A1c level equal to or greater than 8.5%. They were also more likely to be a member of a racial/ethnic minority group and be publicly insured. Missed appointments may be an important indicator of poor treatment adherence, requiring targeted interventions.