Malignant transformation of perineal fistula in Crohn's disease has rarely been reported. We report a case of Crohn's disease with recurrent perineal fistulas. A 36-year-old male, diagnosed with Crohn's disease at the age of 24, developed adenocarcinoma in an anorectal fistula that had existed for years. He was treated with adjuvant chemoradiotherapy but died. A high index of suspicion and regular surveillance is recommended in chronic anorectal fistulas in Crohn's disease. The shorter duration of Crohn's fistulas prior to malignant degeneration necessitates an aggressive approach to rule out cancer.