peer reviewed ; AIMS: To describe the IQED, a quality-assurance system started in 2001 in Belgian hospital-based multidisciplinary diabetes centres, and its effects on the quality of care. METHODS: The study was conducted through four data collections (in 2001, 2002, 2004 and 2006). Approximately 120 diabetes centres provided data on a systematic random sample of 10% of their adult diabetic patients on at least two daily insulin injections. Data on patient characteristics, glycaemic control, cardiovascular risk, diabetes complications, follow-up procedures and treatment were obtained. Local quality promotion was encouraged by returning comprehensive feedback (benchmarks) and during information meetings. RESULTS: Nearly all diabetes centres (98-100%) participated. The pooled sample consisted of 9194 (32%) Type 1 and 19 828 (68%) Type 2 diabetes patients, with mean diabetes duration of 17 years and 14 years, prevalence of microvascular complications of 23% and 38% and prevalence of macrovascular complications of 9% and 26%, respectively. At the start, the quality of care was good in terms of risk-factor testing rates and moderate in terms of patients meeting goals for risk-factor management. At least 50% of the centres initiated quality-promoting initiatives. After 5 years, significant improvements were seen in risk-factor testing rates, apart from renal screening. Improvements in intermediate outcomes were less obvious, apart from an increase in patients reaching the targets for blood pressure and LDL cholesterol. CONCLUSIONS: It is feasible to implement a continuous quality-improvement project on a nationwide scale, with improvements particularly in process indicators.