Large cell neuroendocrine carcinoma (LCNEC) of the urinary bladder are rare. We present a case of a 72-year-old man who presented with back pain and acute renal failure. Ultrasound showed a soft tissue mass in the base of the bladder causing bilateral ureteric obstruction. Subsequent biopsy of this mass demonstrated neuroendocrine carcinoma. He was commenced on neoadjuvant chemotherapy (carboplatin/etoposide) and proceeded to a radical cysto-prostatectomy. Histology revealed a LCNEC involving the bladder, T4a with invasion through to adipose tissue and posteriorly at perivesical resection margins. In addition, there was a Gleason score 9 prostatic adenocarcinoma, distinct from the neuroendocrine carcinoma. Following surgery, the patient developed gross local-regional recurrence and refused further systemic therapy. However, 1 year following referral to palliative care, a further CT-PET showed complete spontaneous remission of his disease. There are only few case reports of LCNEC of the urinary bladder therefore the pathogenesis and treatment protocol are still unclear. This case report highlights the unpredictable nature of this disease.