We have prospectively studied 31 patients who ingested strong alkalis for location, extent, severity, and outcome of the injury to the upper gastrointestinal tract. Alkalis ingested were sodium hydroxide (n = 28) and potassium hydroxide (n = 3). The injury was assessed within 36 h of alkali intake by endoscopy or surgery, or at autopsy. Symptoms and signs did not give a reliable forecast of the extent and severity of injury. The corrosive burns were classified as grade 2a in six patients, grade 2b in eight, and grade 3 in 17. The esophagus was injured in all patients, the stomach in 93.5%, and the duodenum in 29.6%. Acute complications occurred in 32.3% of the patients and death in 12.9%; all but one of such patients had grade 3 burns. All patients with 2a injury recovered without sequelae. Four of the eight patients with grade 2b injury and all survivors of grade 3 injury developed esophageal or gastric cicatrization, or both, which needed endoscopic or surgical treatment. We find endoscopy is not only a safe and reliable tool for diagnosis in such patients, but also is of importance in treatment and prognosis. We conclude that ingestion of strong alkalis is a very serious condition that inflicts severe contiguous injury to the esophagus and stomach and results in high morbidity and mortality.