Every year around March & September/October the CAK Nederland sends out letters to students registered at the municipality telling them to take out basic Dutch health insurance.
If you don’t do anything within three months of receiving this letter you will be fined around €350 – so be sure to react before the deadline! If you have a job beside your studies then you are indeed obliged to take out Dutch health insurance. But if you are only studying and not working in the Netherlands and are insured elsewhere in the EU, then you don’t need to take out Dutch health insurance. You can check this downloadable factsheet to find out for sure if you are required to be insured in the Netherlands specifically. In either case you must react to the letter as soon as possible. All you need to do is fill out this form and send it to the SVB (Sociale Verzekeringsbank).
The SVB will then determine whether you need Dutch health insurance or not and will notify you by post. You will either receive a letter similar to this telling you that you don’t need Dutch health insurance, or you will be informed that you must take out Dutch health insurance.