Rates of obstetric acute renal failure increased significantly in Canada between 2003 and 2010,from 1.66 per 10 000 deliveries in 2003-04 to 2.68 per 10 000 in 2009-10. Rates of admission to an intensive care unit, dialysis, and maternal death among cases of obstetric acute renal failure did not change significantly across this period, suggesting no change in the severity of the renal failure. Although rates of postpartum haemorrhage increased substantially over the same period and hypertensive disorders rose slightly, these rate changes did not explain the increase in rates of obstetric acute renal failure. Theincrease in obstetric acute renal failure was due to a change in rates of this complication in the small (approximately 6%) subpopulation of women with hypertensive disorders of pregnancy, and it was particularly striking among the smaller subset of women with gastational hypertension and significant proteinuria.