Small intestinal bacterial overgrowth (SIBO) is a disorder of excessive bacterial growth in the small intestine, and is often related to chronic diseases like scleroderma, celiac disease, and blind loop syndrome. These bacteria inflame the intestinal mucosa and cause nausea, bloating, vomiting, diarrhea, malnutrition, weight loss and malabsorption. Vitamin B12, iron, and protein deficiencies lead to anemia and hypoalbuminemia. Diagnosis is via the D-xylose test, jejunal aspiration, or gastroscopy and biopsy. Treatment is by addressing the underlying cause and with rifaximin, probiotics, and specific diets.