OBJECTIVE:The purpose of this study was to estimate clinician qualities that influence metabolic outcomes in youth with type 1 diabetes. RESEARCH DESIGN AND METHODS:Data were gathered over two 3 month periods in a large tertiary diabetes center (1500 patients, 8 clinicians) from patients with type 1 diabetes who received continuous care from each clinician. Data included sex, age, diabetes duration, insulin regimen, body mass index (BMI), insulin dose and episodes of severe hypoglycemia. Clinician data included target blood glucose levels, target glycated hemoglobin (HbA1c), Diabetes Attitude Scale and Big 5 Personality Inventory Scale. Mean HbA1c per clinician was the primary outcome variable. RESULTS:The 8 clinicians saw a total of 464 patients during the first time period, and 603 in the second time period. Lowest to highest mean HbA1c per clinician varied by 0.7%. There were small but statistically significant differences between clinicians with their patients' age at diagnosis, duration of diabetes, age, gender, treatment type and BMI SD score. After controlling for these differences, the clinician characteristics that were associated with lower mean HbA1c were having no lower limit in target HbA1c and being self-reportedly "less agreeable." The impact of these clinician attitudinal traits was equivalent to the combined effects of patient characteristics and treatment type. CONCLUSIONS:There was a significant variation in metabolic outcomes between treating clinicians. After controlling for patient clinical differences, clinician mean HbA1c was associated with lower limit in target HbA1c and being "less agreeable." Clinicians who were more demanding and dogmatic appeared to have better outcomes.