We have prospectively evaluated 41 patients who ingested acid for location, extent, severity, and outcome of the injury to the upper gastrointestinal tract. The injury was assessed within 36 h of acid intake by endoscopy or surgery, or at autopsy. Symptoms and signs were unreliable in predicting the extent and severity of injury. The degree of burns was classified as follows: grade 0 in 2 patients, grade 1 in 3, grade 2 in 16, and grade 3 in 20. Esophageal injury was seen in 87.8% of the patients, gastric injury in 85.4%, and duodenal injury in 34.1%. All patients with grade 0, 1, and 2a injury recovered without sequelae. Acute complications occurred in 39.1% of the cases, and death in 12.2%. It is significant that all such patients had grade 3 burns. Five of the 8 patients with grade 2b injury and all survivors of grade 3 injury developed esophageal or gastric cicatrization, or both, which subsequently needed endoscopic or surgical treatment. We find that endoscopy is not only the tool of choice for diagnosis in such cases but also aids in deciding upon treatment and prognosis. We conclude that acid injury of the upper gastrointestinal tract is a very serious condition that affects the esophagus and stomach equally and results in high morbidity and mortality.