Objectives Studies on ethnic disparities in glycaemic control have been contradictory, and compromised by excessively broad categories of ethnicity and inadequate adjustment for socioeconomic differences. We aimed to study the effect of ethnicity on glycaemic control in a large cohort of patients with type 2 diabetes.

Setting We used nationwide data (mainly from primary care) from the Swedish National Diabetes Register (2002–2011) to identify patients with newly diagnosed (within 12 months) type 2 diabetes.

Participants We included 131 935 patients (with 713 495 appointments), representing 10 ethnic groups, who were followed up to 10 years.

Primary and secondary outcome measures Progress of glycated haemoglobin (HbA1c) for up to 10 years was examined. Mixed models were used to correlate ethnicity with HbA1c (mmol/mol). The effect of glycaemic disparities was examined by assessing the risk of developing albuminuria. The impact of ethnicity was compared to that of income, education and physical activity.

Results Immigrants, particularly those of non-Western origin, received glucose-lowering therapy earlier, had 30% more appointments but displayed poorer glycaemic control (2–5 mmol/mol higher HbA1c than native Swedes). Probability of therapy failure was 28–111% higher for non-Western groups than for native Swedes. High-income Western groups remained below the target-level of HbA1c for 4–5 years, whereas non-Western populations never reached the target level. These disparities translated into 51–92% higher risk of developing albuminuria. The impact of ethnicity was greater than the effect of income and education, and equal to the effect of physical activity.

Conclusions Despite earlier pharmacological treatment and more frequent appointments, immigrants of non-Western origin display poorer glycaemic control and this is mirrored in a higher risk of developing albuminuria.