Introduction: Abdominal wall abscesses secondary to fistulating locally advanced colorectal cancer (CRC) is uncommon especially in the context of ulcerative colitis (UC). uncommon. Diagnostic complexity arises in patients with underlying inflammatory bowel disease, particularly ulcerative colitis (UC), in whom fistulisation is uncommon and may influence the extent of surgical resection. Presentation of case: A 49-year-old male with long-standing quiescent ulcerative colitis presented with a recurrent right subcutaneous abscess in the lumbar region. Initial management with incision and drainage failed due to a non-healing wound, prompting further investigation with computed tomography. This revealed a caecal mass with a fistulous tract extending through the posterior abdominal wall. Colonoscopy confirmed a caecal adenocarcinoma. The patient underwent a right hemicolectomy with en bloc excision of the fistulous tract. Histopathology demonstrated a pT3N0 caecal adenocarcinoma with tumour deposits within the tract, confirming external fistulisation. Discussion: This case was diagnostically challenging, with an elusive initial presentation highlighting the atypical manifestations of CRC. UC further confounded the clinical picture, as inflammation in UC is typically confined to the mucosa and does not involve the serosa, making fistula formation exceedingly rare, with only isolated cases reported. There are no consensus guidelines for managing abscess formation and fistulising CRC, and treatment is often individualised based on patient factors and institutional practice. Surgical excision remains the mainstay of management, with multivisceral en bloc resection associated with improved oncological outcomes when an R0 resection is achieved. Conclusion: Ultimately, this case highlights the complexity of CRC presentation and emphasises the need for vigilance when assessing atypical or non-healing soft-tissue infections.