The aim of this study was to develop the Mayo Dysphagia Questionnaire-30 Day (MDQ-30), a tool to measure esophageal dysphagia, by adapting items from validated instruments for use in clinical trials, and assess its feasibility, reproducibility, and concurrent validity. Outpatients referred to endoscopy for dysphagia or seen in a specialty clinic were recruited. Feasibility testing was done to identify problematic items. Reproducibility was measured by test–retest format. Concurrent validity reflects agreement between information gathered in a structured interview versus the patients’ written responses. The MDQ-30, a 28-item instrument, took 10 min (range = 5–30 min) to complete. Four hundred thirty-one outpatients [210 (49%) men; mean age = 61 years] participated. Overall, most concurrent validity κ values for dysphagia were very good to excellent with a median of 0.78 (min 0.28, max 0.95). The majority of reproducibility κ values for dysphagia were moderate to excellent with a median κ value of 0.66 (min 0.07, max 1.0). Overall, concurrent validity and reproducibility κ values for gastroesophageal reflux disease (GERD) symptoms were 0.81 (95% CI = 0.72, 0.91) and 0.66 (95% CI = 0.55, 0.77), respectively. Individual item percent agreement was generally very good to excellent. Internal consistency was excellent. We conclude that the MDQ-30 is an easy-to-complete tool to evaluate reliably dysphagia symptoms over the last 30 days.