Firefighters said a large branch fell on the man, knocking him unconscious and leaving him hanging in a large tree at about 3 p.m. in the 2700-block of Princeton Avenue.
Getting him down from the tree required a joint effort.
"The Evanston people with six or seven vehicles were able to get up there, but they required the Skokie ladder to come from the other side, forming a 'V' so that they could reach the man and bring him down safely," said neighbor John Morrison.
Fire officials said the tree trimmer was trapped more than 20 feet in the air. He was transported to an Evanston hospital in critical condition.