De-tubularised ileum is one of the most common segments used for augmentation cystoplasty. It is associated with complications such as metabolic disturbances, recurrent urinary tract infections, and stone formation. However, adenocarcinoma arising in an augmented bladder is a rare occurrence. We report a 37-year-old female, case of ileocystoplasty 25 years ago due to a thimble bladder (genitourinary tuberculosis) who presented with hematuria for one month. Cystoscopy showed bladder mass in the transposed ileal segments. The patient underwent transurethral resection of the bladder lesion, and the histopathology was suggestive of adenocarcinoma of the ileum. Subsequently, she underwent anterior pelvic exenteration and post-operative recovery was uneventful. The 6-month follow-up showed that the patient was asymptomatic without recurrence. In conclusion, even though adenocarcinoma in the ileal neobladder is rare, life-long with close follow-up with routine cytologic, radiologic, and cystoscopic evaluation for early cancer detection and treatment at an early stage is crucial.