Objective: The aim of this subanalysis of the IMPROVE study was to evaluate the safety and effectiveness of initiating biphasic insulin aspart 30/70 (BIAsp 30) in type 2 diabetes patients uncontrolled on oral antidiabetic drugs (OADs). Methods: IMPROVE is a 26-week, open-label, non-randomised, international observational study in type 2 diabetes patients prescribed BIAsp 30 in routine clinical practice. The total cohort comprised 52 419 patients from various pre-study therapies. Here results from the subgroup of previously insulin-naive patients are reported. Changes in glycated haemoglobin (HbA(1c)), fasting blood glucose (FBG), postprandial blood glucose (PPBG), weight, dose, proportion of patients achieving HbA(1c) <7.0%, and rates of major and minor hypoglycaemic events were recorded. Treatment satisfaction was assessed using a validated questionnaire. Results: A total of 29 160 insulin-naive patients were included; mean age 55.6 years, diabetes duration 7.3 years, baseline HbA(1c) 9.24%. Significant reductions were seen for HbA(1c) (-2.12%; p < 0.0001), FBG (-4.07 mmol/L; p < 0.0001) and PPBG after all meals (mean: -5.27 mmol/L; p < 0.0001); 39.2% of patients achieved HbA(1c) < 7.0% without hypoglycaemia. Better glycaemic control was seen in patients treated with BIAsp 30 twice-daily (BID) both at baseline and final visit, or BID at baseline and three-times daily at final visit, compared with other regimens. The rate of major hypoglycaemic events decreased significantly, while the rate of minor hypoglycaemic events increased. Better glycaemic control and a lower rate of minor hypoglycaemia were observed in patients using BIAsp 30 without OADs than with OADs. There was no clinically relevant change in weight (-0.07 kg; p < 0.0001). At final visit, 59.7% of patients were extremely/very satisfied with treatment, compared with 10.2% at baseline. Conclusions: This open-label, non-randomised, observational study demonstrated that initiating insulin therapy with BIAsp 30 significantly improved glycaemic control in insulin-naive patients previously poorly controlled on OADs. The rate of major hypoglycaemia was reduced and treatment satisfaction increased after initiation of BIAsp 30. Furthermore, better glycaemic control was achieved with BIAsp 30 without OAD compared to with OAD.