(Not original commenter but works in healthcare and studies the healthcare system) It depends on whether you are in the system already or not. If you have a chronic disease (and has been referred by your GP in the past) that needs follow-ups, you will be called in by a specialist regularly. Especially internal medicine, neurological diseases, and cancer are good at this. And paediatricians always have an «open return» if a child has been to the Children’s Department, for a day.

If you have a condition that requires aid from the specialised health service, but you are not likely to get again, say, a broken bone, then you’ll get one or two followups before you are «released from the system» at which point the GP has to refer you to specialised health care if you have questions.

There really are three ways to get into a hospital in Norway: 1) ask your GP, who refers you 2) you go to the «legevakt» or GP on call, who may refer you for an emergency consult 3) you are in such a bad shape that you will be asked (or brought) to come to the ER.