As a PhD student you need health insurance. But Basic health insurance is expensive so there is the option of getting private insurance like from AON.

Right now the College van Zorgevekerers (CVZ) send out a letter in dutch that asks students to get basic health insurance or pay a fine. If you have AON insurance you don’t have to pay the fine but you need to get in contact with them.

Additional Info for Bursary students (by Fabrizio Bianchi):

If you are a bursaal from any country of the European Union, the European Health Insurance Card (EHIC) might be the only thing you need (in Italy for example you get it as long as you are a legal citizen). In case you have to undergo an operation or get any kind of medical assistance, you first have to pay yourself and then have to send the original bill to the AGIS Zorgverzekeringen, who takes care of it for you in the Netherlands, together with a letter in which you explain the situation and a front/rear copy of your EHIC card. The AWBZ Form (here a filled out version from the international student desk (ISD)) has to be completed and sent to:

Sociale Verzekeringsbank
Kantoor Verzekeringen
Postbus 357
1180 AV Amstelveen