OBJECTIVES: To study the transition time of patients with Type 2 diabetes mellitus (T2DM) progressing from “good” to “poor” glycaemic control and its association with the number and type of diabetes-related vascular diseases such as coronary heart disease, stroke, eye complications, peripheral vascular disease and nephropathy.  METHODS: In this retrospective study, data from a disease registry were used.  A cohort of T2DM patients who had attended either a hospital specialist clinic or a primary care diabetes service, and deemed to have “good” control (at least 2 consecutive HbA1c ≤7%) from October 2005 to March 2006 were included in this study. Patients were subsequently followed up for a period of 4 years. Time to “poor” glycaemic control (HbA1c>8%) for each diabetes-related vascular disease was calculated using Kaplan-Meier analysis. Hazards Ratio (HR) was adjusted for age, gender, ethnicity, BMI, duration of diabetes, baseline HbA1c, LDL-cholesterol and insulin use using Multivariate Cox analysis.  RESULTS: There were 7739 T2DM patients, with median age of 68 years and baseline HbA1c of 6.4%. Over a quarter (28.9%) of patients reached “poor” control at the end of 4 years, with a median time of 575 days (95%CI: 550-600). Multivariate Cox regression analysis suggested that likelihood of “poor” control was increased with each additional diabetes-related vascular disease (AdjHR 1.14, 95%CI: 1.07-1.23) and higher for eye complications (AdjHR 1.47, 95%CI: 1.17-1.86) and nephropathy (AdjHR 1.43, 95%CI:1.06-1.93).  CONCLUSIONS: Despite starting with “good” glycaemic control, 3 out of 10 T2DM patients progressed to “poor” glycaemic control at the end of 4 years of study. Patients with more diabetes-related vascular diseases were at higher risk of progressing to “poor” control, particularly those with microvascular complications.  (Word: 271)