To evaluate standards of preventive medical care for Type 2 diabetes in the context of high prevalence and limited resources. Surveys of records for diabetic subjects attending 23 government primary care health centres in Trinidad and Tobago in 2003 and 1998 and nine health centres in 1993. Records were compared by study year for blood glucose and blood pressure, surveillance for complications, appropriate management advice and drug prescriptions. Relevant interventions included new clinical guidelines, training workshops for clinical staff and reports to the Ministry of Health. During this time, investment in primary care increased in the context of health sector reform policies and a favourable macroeconomic environment. Comparing 1993 with 2003, the proportion with a blood glucose test in the past 12 months increased from 33% to 91%, urea or creatinine ever recorded increased from 14% to 61%, diet advice recorded in the first 12 months of follow-up from 35% to 67%, exercise advice from 3% to 61%. The proportion prescribed metformin increased from 25% to 65%, while chlorpropamide decreased from 48% to 0%. The proportion of all subjects treated with antihypertensive drugs increased from 49% to 70%, and the proportion of treated patients prescribed angiotensin-converting enzyme inhibitors increased from 8% to 72%. Most recent ever records of blood glucose, blood pressure and body weight showed no decrease. Repeated surveillance of processes of care provided information to stimulate and plan change. Process changes were associated with intervention at several levels and increased availability of resources.