The Dane County Sheriff's Office says the crash happened shortly before 2 a.m. Saturday in the Township of Westport.
A preliminary investigation shows a 26-year-old man was driving eastbound on State Highway 19 when he missed the curve at Walter Drive. The 2004 Acura hit a mailbox and a large tree then stopped in a farm field.
A 28-year-old man who was a passenger in the front seat died in the crash. Authorities say he was not wearing a seatbelt.
The driver was wearing a seatbelt. He had to be extricated from the vehicle and was flown to the hospital with life threatening injuries.