Ulcerative colitis (UC) is a chronic, relapsing inflammatory bowel disease characterized by continuous mucosal inflammation confined to the colon and rectum. Although fistulizing complications are a hallmark of Crohn's disease, they are exceedingly rare in UC, which typically involves only the mucosal layer. In these rare instances, however, prolonged and severe mucosal inflammation in UC may lead to deeper tissue injury and the development of transmural complications such as fistulas. This report details a case of a 74-year-old female patient, diagnosed with UC two years ago, who presented to our hospital with abdominal pain, mucoid diarrhea, and a lower left quadrant abdominal abscess. After CT-guided drainage of the abscess, a fistulogram confirmed a salpingo-sigmoidal fistula, with contrast outlining a tract from the sigmoid colon to the left fallopian tube and extending into the endometrial cavity. Due to the infrequency of fistula formation in UC, such a presentation can confuse the diagnosis as it does not conform to the classical pattern of UC. Therefore, this case serves to expand our understanding of the disease process and protect against a premature conclusion that would cause UC to be dismissed as a viable diagnosis when fistula formation is seen on initial presentation.