['To compare the quality of care provided by general practitioners participating in diabetes shared-care registers with that provided by GPs not using registers.', 'Cross-sectional comparison using Health Insurance Commission (HIC) data for patients attending the GPs.', '155 GPs using diabetes registers, 459 GPs not using registers, and their patients with diabetes (as identified by HIC criteria). The study analysed data for the period January 1996 to December 1998 and was based on Divisions of General Practice within the South Western Sydney Area Health Service.', 'Frequency of visits to GPs and tests ordered within each of six six-month periods.', 'GPs using the registers had more patients with diabetes, and saw those patients more frequently, than GPs not using registers. "Register" GPs also ordered tests (for HbA(1c) and microalbuminuria) more frequently than "non-register" GPs.'] Does quality of care provided by general practitioners using or not using Division-based diabetes register?