The barium enema is a safe and accurate diagnostic study of the colon but, in rare cases, complications may result. Many of these can be prevented by proper equipment and careful attention to technique. When a complication does occur, prompt recognition and management is vital in decreasing morbidity and mortality. Perforation of the bowel is the most frequent serious complication, occurring in approximately 0.02% to 0.04% of patients. Rarely the colon may burst due to excessive transmural pressure alone. However, a colon weakened by iatrogenic trauma or disease is more likely to perforate during an enema than is a normal healthy bowel. Injury to the rectal mucosa or anal canal due to the enema tip or retention balloon is probably the most common traumatic cause of barium enema perforation. Inflation of a retention balloon within a stricture, neoplasm, inflamed rectum, or colostomy stoma is particularly hazardous. Recent deep biopsy or polypectomy with electrocautery makes the bowel more vulnerable to rupture. The tensile strength of the bowel wall is impaired in elderly patients, patients receiving long-term steroid therapy, and in disease states including neoplasm, diverticulitis, inflammatory bowel disease, and ischemia. Intraperitoneal perforation leads to a severe, acute peritonitis with intravascular volume depletion. The ensuing shock may be rapidly fatal. Prompt fluid replacement and laparotomy are essential. If the patient survives the initial shock and sepsis, later complications caused by dense intraperitoneal adhesions may develop. Extraperitoneal perforation is usually less catastrophic but may result in pain, sepsis, cellulitis, abscess, rectal stricture, or fistula. Intramural extravasation often forms a persistent submucosal barium granuloma which may ulcerate or be mistaken for a neoplasm. The most dramatic complication of barium enema is venous intravasation of barium. Fortunately, this is quite rare as it may be immediately lethal. Most cases have been attributed to trauma from the enema tip or retention balloon, mucosal inflammation, or misplacement of the tip in the vagina. Bacteremia has been found in as many as 23% of patients following barium enema and, in rare cases, may cause symptomatic septicemia. Other less common complications include barium impaction, water intoxication, allergic reactions, and cardiac arrhythmias. Preparatory laxatives and cleansing enemas have been implicated in some instances of dehydration, rectal trauma, water intoxication, and perforation. Careful review of the indications for examination, previous radiographs, and clinical history will identify many of the patients at greater risk for complications so that appropriate precautions may be observed.(ABSTRACT TRUNCATED AT 400 WORDS)