Long-standing Crohn's disease (CD) is well known to be associated with gastrointestinal malignancies. Patients with CD have a higher risk of developing small bowel adenocarcinoma (SBA) compared to healthy individuals. However, CD-associated SBA is not as common as colorectal cancer. While patients with CD often present with complicated stricture lesions in the small intestine, it is difficult to confirm all lesions by endoscopy. There is still no consensus on the surgical treatment of small bowel strictures with suspected CD-associated SBA. We report a case of small bowel high-grade dysplasia and two cases with advanced SBA. Case 1 involved a 53-year-old man whose high-grade dysplastic lesion of the small intestine was discovered incidentally postoperatively and successfully resected curatively. Case 2 was that of a 60-year-old man and Case 3 involved a 69-year-old man. Both patients had multiple small bowel stenotic lesions and were diagnosed with advanced small bowel cancer during follow-up. In conclusion, for patients with long-standing Crohn's disease who are refractory to treatment or have stenotic lesions, surgical resection should be considered as a treatment option with CD-associated SBA in consideration.