Vaccination and health: only if you have traveled to countries at risk of transmission, you must present the "International Certificate of Vaccination against Yellow Fever, CIV", which must be presented in original, be valid and in force. The certificate will be valid ten (10) days after the vaccine is given and will be valid for life.

Countries at risk of transmission: 

• AFRICA: Angola, Benin, Burkina Faso, Cameroon, Democratic Republic of Congo, Gabon, Ghana, Gambia, Guinea. Liberia, Nigeria, Sierra Leone and Sudan.
• SOUTH AMERICA: Bolivia, Venezuela. Brazil, Peru, Colombia, Ecuador, Argentina and Guyana.
• CENTRAL AMERICA: Panama.

Requires a "C" or Consulted Visa.

You will need to apply for a Consulted Visa at one of the Diplomatic Representation of El Salvador abroad or a Consulted Visa to be obtained through the Ministry of Foreign Affairs of El Salvador.

Requirements:

1. Visa application to be made four (4) weeks prior to your planned trip. If the endorser is a juridical person the signature must be legalized relating the corresponding juridical personhood.
2. Photocopy of the used pages of the passport.
3. Photocopy of the ticket quotation or travel itinerary, in which the airline, flight number, date of entry and departure from the Salvadoran territory must be detailed.
4. Hotel reservation if applicable, otherwise specify the place of lodging in the application.
5. Program of activities to be carried out.
6. Financial support for your trip and stay in the country.
7. The visa has a cost of $40 for a single entry.

Form and more details here:
 
Documents to present:

1. Visa stamped type "C".
2. Passport valid for at least six (6) months.
3. Economic solvency.
4. Round trip ticket.
5. Other documents that may be indicated at the embassy or consulate.

More details, here.

More information here.