Appleton police say the shooting happened just before 2 o'clock this morning at the Luna Lounge on the 300 block College avenue.
Officers say the victim was found just inside the Luna Lounge.
They say he was taken to a local hospital with life threatening injuries.
Appleton Police Sergeant Dave Lund says investigators have not identified a suspect.
"Right now we do have our going through the video and also video from the traffic cams that are in downtown Appleton for that intersection," he says.
Investigators say their efforts are complicated by the panic that ensued after the shooting.
"The investigators kind of have to look through the video to see that prior to the shooting, where were these people" Lund says. "Were they in the entry way, were they in the main part of the establishment."
Investigators say a motive isn't clear, but this was not a random act.
"This was targeted against one individual, Lund say "that this wasn't someone that came into the establishment and fired multiple rounds in a general area."
The victim's name has not been released, and the investigation is still ongoing.
If you have any information that could help investigators identify a suspect, you're asked to call Appleton police.