An aviation licence and medical certificate together give the right to act as a flight crew and  air traffic controller.
The holder of a medical certificate must be mentally and physically fit to exercise safely the privileges of  the applicable licence.
To obtain a medical certificate, the applicant must pass an aeromedical examination and meet the medical requirements applicable to the licence sought.
Medical certificates are for flight crew  issued, renewed and revalidated in accordance with “Regulation of the Flight Crew“ (Official Gazette RS“, No. 33/13).
Classes of the medical certificates for flight crew:
Class 1 medical certificate for holders of ATPL and CPL licences 
Class 2 medical certificate for holders of PPL(A), PPL(H), SPL and BPL private pilot licences 
Class LAPL (Light Aircraft Pilot License) medical certificate for holders of LAPL(A/H/S/B) licences
Class 3 - Air traffic controllers
Medical certificates are for air traffic controllers issued, renewed and revalidated in accordance with 
Regulation on air traffic controller`s licences, training organisations and aero-medical centres ("Official Gazette of the Republic of Serbia", No 83/15); based  on COMMISSION REGULATION (EU) 2015/340 of 20 February 2015. 
An aeromedical examination for revalidation may be made 6 weeks before the medical certificate expires.
For revalidation of a current medical certificate, an aeromedical examination may be carried out 45 days (six weeks) before the certificate expires, in which case the validity period of the new certificate is still calculated from the expiry date of the previous medical certificate.