Police Scotland said they were called to the scene, near the Murcar roundabout, at about 09:15 on Saturday morning.
A spokesman said the drivers of both vehicles had been taken to hospital with serious injuries.
The road was closed northbound for several hours to allow officers to deal with the aftermath of the crash.
Police have appealed for witnesses.
Sgt Steve Manson said: "A southbound grey Vauxhall Astra motor car and a northbound silver BMW 320 motor car collided head-on resulting in the drivers, and only occupants, of both vehicles having to be cut free by the Scottish Fire and Rescue Service.
"Both were taken to hospital with serious injuries."
Two people have been injured after a head-on crash on the A90 at Bridge of Don.