EU students often treat their EHIC as settled cover for the whole degree, which holds only for as long as studying is all they do. A few hours of paid work a week is enough to move them into the Dutch insurance obligation, and nobody announces the switch.
For pure studying, yes — your EHIC (issued by your home country's insurer) covers necessary medical care while you're temporarily living in the Netherlands as a student, and Dutch basic insurance isn't even open to you during that period. It's not travel insurance with a time limit; it's your home social-security system extending cover abroad, so confirm with your home insurer that it stays valid for your whole study duration, not just short trips. What changes things is work. Once you take a paid job or paid internship in the Netherlands, EHIC stops being sufficient the moment that work starts — you become subject to the Dutch insurance obligation and need a Dutch basisverzekering (basic policy) within four months, same as any other worker. This catches people out because the switch isn't flagged anywhere; it's on you to notice. A small side job of just a few hours a week still counts — there's no minimum-hours exemption for EU students the way there's a permit threshold for non-EU students. An unpaid, curriculum-required internship generally doesn't trigger the obligation, but a paid one does. When your status changes, register the Dutch policy promptly to avoid owing backdated premiums.