The effectiveness of cimetidine (30-40 mg/kg/day) was evaluated in 32 children with gastroesophageal reflux disease complicated by esophagitis who entered a random double-blind trial for 12 weeks. Esophagitis was diagnosed in all patients by endoscopy with biopsy. Seventeen patients (age, mean +/- SD: 21.7 +/- 37.65 months) received cimetidine (c-pts), and 15 (age, mean +/- SD: 29.03 +/- 39.73 months) received a placebo (p-pts). All patients received intensive postural therapy. Based on clinical and endoscopic (and histologic) data, 12 c-pts and three p-pts were healed (p less than 0.01), the condition of four c-pts and three p-pts had improved (not statistically significant), and the condition of one c-pt and nine p-pts had worsened (p less than 0.01). Both clinical and esophagitis scores significantly decreased only in the c-pt group, as compared with p-pts. Improvement of esophagitis was seen in all (100%) of c-pts with mild or moderate esophagitis versus 57.14% of p-pts (p less than 0.01) and in 87.5% of c-pts with severe esophagitis as compared with 25% of the p-pt group (p less than 0.01). We conclude that cimetidine is an effective agent for treatment of reflux esophagitis in children. Although gastroesophageal reflux disease in infancy has a naturally self-limited course with conservative care (thickened feedings and posture adjustment), extensive pharmacologic therapy is needed in the presence of esophagitis.