Common symptoms of gastroparesis include nausea, vomiting, early satiety, postprandial fullness, and upper abdominal pain. Domperidone is used for treatment of gastroparesis. Daily symptom scoring may help document efficacy. Aim To determine the effectiveness of domperidone for gastroparesis symptoms using the gastroparesis cardinal symptom index‐daily diary (GCSI‐DD) and to determine which symptoms improve and when with domperidone treatment. Methods Symptomatic patients with diabetic or idiopathic gastroparesis were enrolled. Gastric emptying was performed using 4 hour scintigraphy. GCSI‐DD recorded symptoms at baseline and during six weeks of treatment with domperidone 10 mg TID. GCSI‐DD records severity of nausea, early satiety, postprandial fullness, upper abdominal pain, overall gastroparesis symptoms on a scale of 0 (no symptom) to 4 (very severe) and records the number of vomiting episodes per day. Results Thirty‐four patients with gastroparesis (5 diabetic, 29 idiopathic) participated in this open label study. Treatment duration averaged 36.9 ± 7.6 days. Improvement in overall gastroparesis symptoms occurred on day 3 of treatment and maintained during the treatment. Early satiety, postprandial fullness, and overall symptom severity significantly improved from baseline to the final week of treatment (P < .05 for all), whereas nausea had borderline improvement (P = .055). Side effects included palpitations (5 patients), headache (5), breast tenderness (2), menstrual bleeding (2), dizziness (1), drowsiness (1), chest pain (1), swelling (1), constipation (1). Conclusions Domperidone improves symptoms of gastroparesis, reducing overall gastroparesis symptom severity and decreasing early satiety, postprandial fullness, and nausea. GCSI‐DD is useful to document efficacy of therapy for gastroparesis. Therapeutic response to domperidone in gastroparesis: A prospective study using the GCSI‐daily diary. The figure shows the mean daily symptom scores during the initial two weeks of treatment as recorded in the GCSI‐DD.