Lange, who has battled weight issues and an addiction to drugs for years, was hospitalized during the weekend for undisclosed reasons.
The Post said his mother stopped by his New Jersey apartment last Saturday to bring him food and found him bleeding heavily from self-inflicted wounds.
She called 911 and Lange was transported to a hospital where he was treated for six "hesitation wounds" and three deep incisions, the source said.
The Post did not say what his current condition is.
"We all have our demons," Howard Stern said about his frequent radio-show sidekick this week. "Artie has given this show tremendous moments of great comedy. He's a tremendous contributor. He is a good man. Don't forget how great he is."