Cases of giant vesical diverticula that cause defecation disturbance are very rare. A 67-year-old man with such a condition was admitted to our hospital complaining of pollakiuria , nycturia , retardation, two-phase urination and defecation disturbance which began about 7 years earlier. A goose-egg-sized tumor touched above the hen-egg-sized prostate and the tumor disappeared after urination. X-ray examinations revealed that defecation disturbance was caused when the sigmoid colon was oppressed by the giant diverticulum. After diverticulectomy and prostatectomy the vesical symptoms and defecation disturbance completely subsided.