A 36–year–old man was referred to our hospital after developing dull lower abdominal pain, pneumaturia, and fecaluria. He had a history of acute appendicitis treated without surgery at the age of 6, and had since experienced recurrent episodes of cystitis, pneumaturia, and fecaluria. Escherichia coli was cultured from the urine. Abdominal CT and MRI suggested an enterovesical fistula. Cystoscopy revealed a stone in the bladder, for which lithotripsy was performed. An unusual dilation of the appendix orifice was found on colonoscopy. Retrograde cystography did not show an enterovesical fistula ; however, a small bowel series using an ileus tube revealed an appendicovesical fistula. The patient therefore underwent surgery and the fistula was found between the right side of the bladder dome and the middle of the appendix. Appendectomy with partial cystectomy including the fistula was performed. We concluded that the appendicovesical fistula might have developed after appendicitis at the age of 6 and that the diagnosis could have been delayed for as long as 30 years because the fistula was well established. Appendicovesical fistula is a rare condition, generally forming after appendicitis. Direct imaging of the fistulous tract is not easy, and the fistula often takes a long time to diagnose. However, the diagnosis can be made if specific findings are present, and the disease is completely curable by operation.