Portal vein thrombosis occurred in a patient who bled from gastric varices that developed after obliteration of esophageal varices by endoscopic sclerotherapy. This complication was recognized only at surgery when thrombectomy and endovenectomy preceded the successful placement of an end-to-side portocaval shunt. At histopathology, the presence of an amorphous, eosinophilic material staining negatively for fibrin and similar to sclerosant injected at sclerotherapy was observed within the clot. This latter finding, previously unreported, provides convincing evidence for the causal relationship of portal vein thrombosis to endoscopic sclerotherapy.