In the province of Manitoba, the incidence of preterm birth has been increasing and the rate is higher among Aboriginal than non-Aboriginal women. The purpose of this study was to identify risk factors for spontaneous preterm birth in Manitoba women, and to compare risk factors among Aboriginal and non-Aboriginal women. A case-control study was performed at two tertiary care hospitals in Winnipeg, Manitoba, Canada from October 1999 to December 2000. Cases delivered a live singleton infant at