Use of the DASH (Dietary Approaches to Stop Hypertension) diet, which is rich in fruits, vegetables, and low-fat dairy foods, significantly lowers blood pressure. Among the 459 participants in the DASH Trial, 72 had stage 1 isolated systolic hypertension (ISH) (systolic blood pressure, 140 to 159 mm Hg; diastolic blood pressure, <90 mm Hg). We examined the blood pressure response in these 72 participants to determine whether the DASH diet is an effective treatment for stage 1 ISH. After a 3-week run-in period on a typical American (control) diet, participants were randomly assigned for 8 weeks to 1 of 3 diets: a continuation of the control diet (n=25), a diet rich in fruits and vegetables (n=24), or the DASH diet (n=23). Sodium content was the same in the 3 diets, and caloric intake was adjusted during the trial to prevent weight change. Blood pressure was measured at baseline and at the end of the 8-week intervention period with standard sphygmomanometry. Use of the DASH diet significantly lowered systolic blood pressure compared with the control diet (-11.2 mm Hg; 95% confidence interval, -6.1 to -16.2 mm Hg; P<0.001) and the fruits/vegetables diet (-8.0 mm Hg; 95% confidence interval, -2.5 to -13.4 mm Hg; P<0.01). Overall, blood pressure in the DASH group fell from 146/85 to 134/82 mm Hg. Similar results were observed with 24-hour ambulatory blood pressure measurements. In the DASH diet group, 18 of 23 participants (78%) reduced their systolic blood pressure to <140 mm Hg, compared with 24% and 50% in the control and fruits/vegetables groups, respectively. Our results indicate that the DASH diet, which is rich in fruits, vegetables, and low-fat dairy foods, is effective as first-line therapy in stage 1 ISH.