The predominant electrolyte imbalance associated with enterourinary fistulas is hyperchloremic acidosis. The mechanism is the absorption of urinary electrolytes across the colonic mucosa. One of the genitourinary associated anomalies of a high imperforate anus is a rectourinary fistula. There have been 5 cases of hyperchloremic acidosis as a complication of an imperforate anus with a rectourinary fistula reported in the literature to date. An additional case is presented with a clinical analysis of the previously reported cases. The important factors in the development of hyperchloremic acidosis in patients with an imperforate anus are 1) the presence of a rectourinary fistula, 2) an initial diverting colostomy permitting a long segment of colonic mucosa for the absorption of urinary electrolytes, 3) distal urinary tract obstruction allowing significant volumes of urine to flow into the colonic segment and 4) the presence of urinary tract infection contributing to the urinary obstruction. Management should consist of vigorous electrolyte therapy, decreasing the retrograde flow of urine into the colon by temporary catheterization and early repair of the fistulous tract.