Aims/hypothesis This study was performed to evaluate the influence of ethnicity and socioeconomic status (SES) on metabolic control in a population-based cohort of children with type 1 diabetes mellitus, and to evaluate whether any relationship between ethnicity and HbA 1c is mediated by SES. Methods We performed a retrospective review of all patients under age 16 years with type 1 diabetes (n=555) from 1995 to 2005 in the greater Auckland region, New Zealand. Diabetes care variables and HbA 1c values were collected prospectively, during clinic visits. Results The mean population HbA 1c was 8.3±1.3%. Maori and Pacific patients had poorer metabolic control than their European counterparts (9.1% and 9.3% vs 8.1%, p<0.001) and higher rates of moderate to severe hypoglycaemia (31.1 and 24.8 vs 14.9 events/100 patient-years, p=0.03). In multiple linear regression analysis, both ethnicity and SES were independently associated with HbA 1c (p<0.001). Other factors associated with higher HbA 1c level were longer duration of diabetes, higher insulin dose, lower BMI z score and less frequent blood glucose monitoring (p<0.001).Conclusions/interpretation Both ethnicity and SES independently influenced metabolic control in a large, unselected population of children with type 1 diabetes. Irrespective of SES, Maori and Pacific youth with type 1 diabetes were at greater risk of both moderate to severe hypoglycaemia and long-term complications associated with poor metabolic control.