If you want to go to Greece for treatment and stay there for less than 90 days, you need to issue a short-term visa type C.

If your medical therapy or treatment is expected to last longer than 90 days, you should instead apply for a national (long-term) type D visa for medical treatment in the relevant country, which allows you to stay longer.

Patients from third countries that have not reached a visa-free agreement with the members of the Schengen area must obtain this visa before flying to any of the Schengen countries.

The list of countries whose citizens need a visa is here:

https://www.schengenvisainfo.com/who-needs-schengen-visa/ 

What documents are required to obtain a Schengen visa for medical reasons?

Necessary documents for obtaining a Schengen visa for treatment:

• Visa application form. Fill in all the required information correctly in the short-term visa application form. Don't forget to sign the form at the end after you print it.

An example of a form to fill out: https://www.schengenvisainfo.com/download-schengen-visa-application-form/ 

• Two photos. These photos must be identical and not older than three months, meet the Schengen criteria for visa photos.

Photo criteria here:

https://www.schengenvisainfo.com/schengen-visa-application-requirements/photo-requirements/ 

• Valid travel document/passport. Make sure your passport was issued within the last ten years and is still valid for three months after your planned departure from the Schengen area.

• A copy of the data page of your passport.

• Round-trip ticket booking. A document that contains details of your flight to and from the Schengen area, including flight numbers and dates.

Information on booking round-trip tickets here:

https://www.schengenvisainfo.com/flight-itinerary-visa-application/ 

• Tourist medical insurance. Coverage of the entire Schengen area with a minimum coverage of EUR 30,000 for the entire period of stay.

Detailed information about insurance here:

https://www.schengenvisainfo.com/schengen-visa-insurance/ 

• Proof of residence. It can be any of the following: Confirmed residency in a medical clinic/hospital, Hotel reservation, Invitation letter, Lease agreement.

• Document confirming marital status: marriage certificate, birth certificate of children, death certificate of spouse, if any.

• Confirmation of paid fee. It is 90 euros for adults, but for children and some categories the price is less or reduced. To know more, check the list of Schengen visa fees here:

https://www.schengenvisainfo.com/schengen-visa-fee/  

• Proof of financial capabilities. Evidence that the applicant has sufficient financial means to pay for medical expenses and other related expenses during the entire period of treatment. It can be one of the following: Bank statements, Sponsorship letter + statement from the sponsor's bank account, Confirmation of advance payments for treatment + bank statements about other related expenses.

• Verbal note (this is an unsigned diplomatic memorandum that serves as an informal reminder of an unanswered question or request) from the Ministry of Health of the applicant's country of residence. If the Ministry of Health in your country will cover the cost of your treatment, a letter stating that the government is willing to cover the cost of your treatment should be provided.