Police are appealing for witnesses after a collision on the A351 near the Bakers Arms roundabout at 4:26pm, Sunday 9 June.
The collision was between a Honda motorcycle, a Honda CR-V car and a Mercedes Sprinter van.
The rider of the motorcycle was airlifted to Southampton General Hospital with life-changing injuries; no one else was injured.
Road closures were in place between the Bakers Arms and the Holton Heath roundabouts so that investigators could examine the scene, these ended just after 7pm.
Inspector Joe Pardey, of the traffic unit, said: “I am appealing to anyone who witnessed the collision or saw the manner of driving or riding immediately prior to the incident to please call Dorset Police.
“I am also keen to hear from anyone who may have any relevant dashcam footage.
“Finally, I would like to thank motorists for their patience and understanding during the road closure, which was entirely necessary to allow us to examine the scene and treat the injured rider.”
Anyone with information should contact Dorset Police via their website, at SCIT@dorset.pnn.police.uk or call 101 and quote incident number 9:322.
Alternatively, you can contact Crimestoppers anonymously on 0800 555 111 or at their website.