Healthcare in Sweden is very expensive if you are not covered by some kind of insurance. If your spouse/cohabitant and/or children accompany you to Sweden, they too need to ensure that they have some form of healthcare cover in Sweden. You can down-load an informative paper from Försäkringskassan, The Social Insurance Office. If you are not registered at Försäkringskassan you could sign an insurance via Kammarkollegiet (to a cost of 10 sek per day). NB! Check first with your host institution as they might have an insurance signed for all incoming researchers.

If you are an EU/EEA or Swiss citizen

You are covered as soon as you register as resident with the Swedish Migration Board. Your entitlement to some benefits (for example, sickness benefit) depends on whether or not you are working, and paying taxes, in Sweden.

If you are a citizen of a Nordic country

You are automatically covered at all times.

If you need a visa to enter Sweden ...

As part of your application you will be required to show you are covered by a medical insurance plan for the duration of your stay.

... and your residence permit is for less than a year

You cannot be listed in the Swedish civil registry, which renders you ineligible for Swedish healthcare benefits. In this case you also need to make arrangements for health insurance cover for the duration of your stay in Sweden before you arrive, either with an insurance company in your home country or else through an arrangement with the institution at which you will be working in Sweden. However, foreign citizens may be eligible to medical benefits under certain conditions. Check with your home Social Security or Insurance Office before you leave.

... or you have a residence permit for a year or more

You are eligible for the same healthcare benefits as Swedes. However, you are not covered until you register at a local tax office. You should therefore get some form of travel/medical insurance in your home country for your first few days in Sweden. If you will receive a scholarship or stipend (other than from a Marie Curie fellowship) it means that you will not pay tax in Sweden. In this case there might be some restrictions in the social security such as sick leave allowance (80% of your income) and parental leave allowance. This applies even if your stay is for a year or longer.

Here is a useful link to EUlisses giving EU information on social security.