BACKGROUND: Because uncontrolled echocardiographic surveys suggested that up to 30% to 38% of users of fenfluramine and dexfenfluramine had valvular disease, these drugs were withdrawn from the market. OBJECTIVE: To determine the risk for new or worsening valvular abnormalities among users of fenfluramine or dexfenfluramine who underwent echocardiography before they began to take these medications. DESIGN: Cohort study. SETTING: Academic primary care practices. PATIENTS: 46 patients who used fenfluramine or dexfenfluramine for 14 days or more and had echocardiograms obtained before therapy. MEASUREMENTS: Follow-up echocardiography. The primary outcome was new or worsening valvulopathy, defined as progression of either aortic or mitral regurgitation by at least one degree of severity and disease that met U.S. Food and Drug Administration criteria (at least mild aortic regurgitation or moderate mitral regurgitation). RESULTS: Two patients (4.3% [95% CI, 0.6% to 14.8%]) receiving fenfluramine-phentermine developed valvular heart disease. One had baseline bicuspid aortic valve and mild aortic regurgitation that progressed to moderate regurgitation. The second patient developed new moderate aortic insufficiency. CONCLUSION: Users of diet medications are at risk for valvular heart disease. However, the incidence may be lower than that reported previously.