Inflammatory bowel diseases are chronic disorders of the gastrointestinal tract that include Crohn's disease (CD), ulcerative colitis (UC) and inflammatory bowel disease-unclassified (IBDU). The latter defines a subgroup of patients with clinical and endoscopic evidence of chronic colitis, without specific features of either CD or UC. These patients will possibly be re-classified as having UC or CD during the follow-up, although a significant percentage of them will keep the diagnosis of IBDU. IBDU is the rarest subtype of IBD, both in children and in adults, although it is twice as common among the pediatric population, especially in the younger ages. The diagnosis can only be made after a comprehensive diagnostic work-up, combining clinical history, physical and laboratory examination, upper and lower gastrointestinal endoscopy, with histology and imaging of the small bowel. The therapeutic strategy is borrowed from that of UC and CD, although recent data suggest that IBDU has a lower therapeutic burden with a generally mild disease course and a good response to mesalamine. Since there are only few published data on pediatric IBDU, and no guidelines on its management are available, this review aims at summarizing the most recent evidence for the diagnostic work-up with a specific focus on medical and surgical options in the treatment of IBDU.