OBJECTIVE - To investigate whether blood pressure is different in type 2 diabetic patients on a diet rich in carbohydrates versus a diet rich in cis-monounsaturated fatty acids. Data on the dietary effects on these diets' glucose and lipid metabolism have been previously published. RESEARCH DESIGN AND METHODS - The study compared the effect of feeding 42 type 2 diabetic patients a carefully controlled isoenergic high-carbohydrate (high-carb; 55% energy as carbohydrate, 30% as fat, and 10% as monounsaturated fat) and high-monounsaturated fat (high-mono; 45% energy as fat, 25% as monounsaturated fat, and 40% as carbohydrate) diet for 6 weeks each in a four-center, randomized, cross-over study on blood pressure. Twenty-one patients continued the diet they received during the second phase for an additional 8 weeks. RESULTS - According to repeated-measures ANOVA, blood pressure during the last 3 days of each phase was similar after 6 weeks of the high-carb and high-mono diets (systolic blood pressure: 128 ± 16 vs. 127 ± 15 mmHg, P = 0.9; diastolic blood pressure: 75 ± 7 vs. 75 ± 8 mmHg, P = 0.7). However, after 14 weeks of the high-carb diet (n = 13), there was a significant increase in blood pressure compared with 6 weeks of the high-mono diet (systolic blood pressure: 132 ± 13 vs. 126 ± 11 mmHg, P = 0.04; diastolic blood pressure: 83 ± 6 vs. 76 ± 7 mmHg, P = 0.002). After 14 weeks of the high-mono diet (n = 8), the reduction in blood pressure was not significant compared with 6 weeks of the high-carb diet (systolic blood pressure: 118 ± 14 vs. 121 ± 16 mmHg, P = 0.4; diastolic blood pressure: 71 ± 8 vs. 75 ± 10 mmHg, P = 0.3). CONCLUSION - Although the exchange of carbohydrates with monounsaturated fats may not affect blood pressure in the short term, long-term consumption of a high-carbohydrate diet may modestly raise blood pressure in type 2 diabetic patients.