Diagnosing Crohn's disease in the small intestine can be troublesome. Traditionally, the small bowel is evaluated by ileocolonoscopy and small bowel follow-through or enteroclysis. In recent years MRI, CT, ultrasound and capsule endoscopy have emerged. All are validated and implemented in clinical practice. Double-balloon enteroscopy, PET-CT and SPECT are newer methods, which are still being evaluated in clinical trials. The purpose of this article is to review clinical studies focusing on the validity of modalities for diagnosing Crohn's disease of the small intestine.