Serum cholinesterase activity was measured in diabetes, hypertensive and diabetic/hypertensive patients. The sample consisted of volunteer patients and was divided in a control group (n=26), type 2 diabetic group (n=16), hypertensive group (n=12) and type 2 diabetic/hypertensive group (n=26). In addition, blood glucose, cholesterol and triglyceride levels were determined. Serum cholinesterase activity in the control group was significantly lower in relation to the other groups (p<0.001). Blood glucose levels were elevated in type 2 diabetic and type 2 diabetic/hypertensive groups. In vitro studies showed increased cholinesterase activity in the presence of glucose 5-100mM or insulin 0.5-25 UI (p<0.001). Cholesterol and triglycerides were at normal levels only in the control group. Possibly, a relationship exists between the increase in serum cholinesterase and the vascular complications in the diabetic patients, potentially stimulated by the levels of glycemia and dyslipidemia. Although patients were receiving different medicines, the increase in enzyme activity was similar in all groups. This enzymatic profile suggests a possible interference of the diseases in the catalytic mechanism of the serum cholinesterase enzyme.