Inflammatory bowel disease (IBD), which includes Crohn's disease (CD) and ulcerative colitis (UC), is chronic in nature and is characterized by abdominal pain, diarrhea, bleeding, and malabsorption. It is considered a complex multigenic and multifactorial disorder that results from disturbed interactions between the immune system and commensal bacteria of the gut. Recent work has demonstrated that IBD with an early‐onset within the first months of life can be monogenic: mutations in IL‐10 or its receptor lead to a loss of IL‐10 function and cause severe intractable enterocolitis in infants and small children. Both IL‐10 and IL‐10 receptor deficiency can be successfully treated by hematopoietic stem cell transplantation.