Two women were killed and three men injured when the van they were in rolled on Interstate 90 west of Butte, the Highway Patrol said.
Sheila Morris, 20, of Spokane, was driving when the accident occurred about 8 a.m. and died a short time later at St. James Community Hospital.
A passenger, 19-year-old Heather Wilson of Seattle, died at the hospital a few hours later, said Butte-Silverbow County Coroner Lee LaBreche.
The patrol said the van drifted off the right side of the pavement and Morris overcorrected into the median where the vehicle rolled several times.
Patrolman John Stewart said four of the five people were ejected from the rolling vehicle.