CONTEXT: Caustic substances cause tissue destruction through liquefaction or coagulation reactions and the intensity of destruction depends on the type, concentration, time of contact and amount of the substance ingested. OBJECTIVES: To analyze the complications in patients who ingested caustic substances and correlate them with the amount of caustic soda ingested. DESIGN: Retrospective study. SETTING: University hospital, a referral center. PARTICIPANTS: A total of 239 patients who ingested caustic soda. MAIN MEASUREMENTS: The amount of granulated caustic substance ingested was measured as tablespoonfuls and the following complications were analyzed: esophagitis, esophageal stenosis and progression to cancer, fistulas, perforations, stomach lesions, brain abscesses, and death. Stenosis was classified as mild, moderate or severe according to the radiological findings. RESULTS: We observed an 89.3 % incidence of esophagitis; 72.6 % of the cases involved progression to stenosis and 1 per cent died during the acute phase. Stenosis was mild in 17.6 % of cases, moderate in 59.3 % and severe in 23 %. The incidence of stenosis was 80.8 per cent in women and 62.5 % in men. The incidence of stenosis was 46.9 % in the group that ingested "fragments" and 93.6 % in the group that ingested one or more tablespoonfuls of caustic substances. Among subjects who ingested one or more tablespoonfuls, 32.2 % developed lesions of the stomach-duodenum, whereas the ingestion of "fragments" was not sufficient to induce these lesions. There was no correlation between the intensity of lesions of the esophagus and of the stomach. Progression to cancer of the esophagus occurred in 1.8 % of cases, death during the chronic phase in 1.4 %, perforations in 4.6 %, fistulas in 0.9 %, and brain abscesses in 1.4 %. CONCLUSIONS: The complications were related to the amount of caustic soda ingested. Small amounts caused esophagitis or stenosis and large amounts increased the risk of fistulas, perforations and death.