A man lived for several years totally unaware a bullet was lodged in his head after a drunken New Year's Eve night out.

It wasn't until the Polish construction worker, who lives in Germany, noticed a cyst on his head and went to hospital that the truth was revealed - x-rays showed there was a 5.6mm 22-calibre bullet lodged in the 35-year-old's scalp.

The man couldn't quite remember whether it was 2004 or 2005, but did recall feeling a forceful blow to the back of his head around midnight as he celebrated New Year's Eve in the German city of Herne, police spokesman Volker Schutte told German English-language newspaper The Local.

"He told us he remembered having a sore head, but that he wasn't really one for going to the doctor," he said.

The wound later healed around the bullet and it was not until the man decided to have the lump examined due to recurring pains that the discovery was made.

"He must really have a strong constitution," said Mr Schutte, who spoke to the man while he recovered in hospital after an operation on Friday.

"He was of course intoxicated at the time he felt the blow. It was New Year's Eve so naturally he'd had a bit more than usual to drink." Mr Schutte told the paper.

"The key, and this is obviously important and good for this man, is that the power behind the bullet was low," said Mr Schutte. "Otherwise he would have sustained much more severe injuries."

Doctors informed police immediately after the bullet was discovered, and they are now searching for the shooter, who if found will face charges of negligent bodily harm.

Investigators believe that someone likely rang in the New Year with a shot, unintentionally hitting the man, The Local reported.

While police admit the chances of finding the culprit are not great, Mr Schutte said the incident may serve as a warning to others.

"Our next pre-New Year's Eve safety campaign will now have an argument for telling people to leave their pistols in the gun safe because they'll see what kind of damage can be done," he told the paper.

As for the patient, he is expected to make a full recovery and will be released from hospital in the next few days.

- NZ Herald staff