Case: We present a case of spontaneous extra-peritoneal rupture of an acquired diverticulum an elderly male with symptoms of bladder outlet obstruction who presented in emergency with acute abdomen. Outcome: The acute phase was managed conservatively with bladder drainage and intravenous antibiotics. He recently underwent Transurethral Resection of Prostate. He is asymptomatic on follow-up. Conclusions: Acquired bladder diverticulum are rare in adults and are mostly seen in patients with high pressure bladder due to bladder outlet obstruction. Atraumatic extraperitoneal ruptures of diverticulum are uncommonly reported.