A 38-year-old woman (gravida 4, para 1) underwent arteriography at 19 weeks' gestation after two exploratory laparotomies had failed to identify a source of retroperitoneal and intraabdominal hemorrhage. The arteriogram demonstrated a large right renal artery aneurysm (RAA) and a very small left RAA. Emergency repair of the aneurysm was attempted but was impossible, so a right nephrectomy was performed. The fetus had died prior to arteriography and a cesarean section was performed concomitantly. The postoperative course was unremarkable. RAAs are rare and usually asymptomatic, but pregnancy is associated with a higher risk of rupture. Prior to 1970, reported rupture occurred most often on the left side, during the third trimester, and was associated with a 92% maternal mortality and a 100% fetal mortality rate. Since 1970, published reports have not shown a left-sided predominance, and survival after this catastrophic event has greatly improved, even though preoperative diagnosis is still rare. The possibility of a ruptured RAA should be considered in pregnant women with evidence of retroperitoneal hemorrhage. Arterial repair should be attempted but has not been feasible in most cases. This case was unusual because it occurred during the second trimester of pregnancy. Recent cases and technical considerations regarding repair are discussed.