Good physical and mental health is a prerequisite for anyone planning to scuba dive. A fitness to dive certificate for those willing to enter a scuba diving course as well as for amateur or professional divers can only be issued if there are no medical contraindications to dive. It is usually within the responsibility of a diving instructor, a manager of underwater work or a physician to assess a person’s mental and physical health and grant them permission to stay under hyperbaric conditions. The legal requirements for issuing a fitness to dive certificate are different for recreational and professional divers. The article discusses the issues related to medical assessment of fitness to dive for recreational, professional and military divers. It also discusses contraindications to scuba diving and guidelines for diving fitness health assessment in divers with a history of a diving‑related condition.