Small intestinal bacterial overgrowth (SIBO) is a medical condition in which bacteria that are normally present in small bowel overgrow, and cause symptoms like bloating, abdominal pain, chronic diarrhea, and malnutrition. SIBO 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 with rifaximin, probiotics, and specific diets.