The IMPROVE (TM) observational study evaluated the safety profile and effectiveness of biphasic insulin aspart 30/70 (BIAsp 30) in patients with type 2 diabetes in routine practice in 11 countries. Patients who initiated insulin therapy with, or switched existing insulin therapy to, BIAsp 30 in routine care were eligible for this 26-week, non-interventional observational study. Data on adverse events, hypoglycaemia and glycaemic parameters were obtained from patients' diaries and medical notes. Questionnaire-based patient treatment satisfaction was also measured. We report global results and, uniquely for a diabetes observational study, country-specific data. A total of 52,419 patients were enrolled from three prestudy treatment groups: no pharmaceutical therapy (n = 8966, diabetes duration 2.0 years, baseline HbA(1c) 9.9%), oral antidiabetic drugs (OADs) only (n = 33,797, diabetes duration 7.4 years, baseline HbA(1c) 9.2%) and insulin +/- OADs (n = 9568, diabetes duration 10.4 years, baseline HbA(1c) 9.3%). At final visit, HbA(1c), fasting and postprandial blood glucose were significantly reduced from baseline in all subgroups (no pharmaceutical therapy: -3.1%, -5.9 and -9.0 mmol/l, respectively; OADs-only: -2.1%, -4.1 and -6.1 mmol/l; insulin +/- OADs: -2.0%, -3.3 and -5.1 mmol/l). Major hypoglycaemia rates decreased in all subgroups; minor hypoglycaemia increased in the insulin-naive groups. There was no mean weight gain across subgroups. Across all countries, glycaemic parameters and major hypoglycaemia were reduced; weight increases were seen in some countries. Treatment satisfaction increased in all subgroups and countries following BIAsp 30 therapy. Initiating insulin with, or switching insulin therapy to, BIAsp 30 in routine care resulted in improved glycaemic control, reduced major hypoglycaemia and greater treatment satisfaction.