Koh Samui Medical Facilities
It is fair to say that most modern medical facilities are available on Koh Samui but more serious injuries are normally transferred to Bangkok.
Generally
There are a range of government and prvate medical facilities available on Koh Samui. Most toursits have travel insurance and in the case of emergencies visit the private hospitals and dentists. The Government facilities are mainly for the locals.
Hospitals
Koh Samui Hospital is the government hospital. There are also four international private hospitals on the island. Private general practices are less of a familiar sight in Thailand than they are in the west. If you need to see a doctor while on Samui then head for a hospital. Hospitals on the island vary hugely in the prices they charge, so it pays to ask a local for a recommendation or contact the hospital and check about prices. The hospitals also offer health checks. Be aware that in most cases you'll be asked to pay by cash/credit for out-patient treatments, unless you contact your insurance first. For motor bike accidents (extremely common on the island) insurance is often invalidated by the size of a motorbike's engine, the lack of an appropriate license or simply by the fact you were riding one in the first place. Check the small print on your policy. Despite all their promises, insurance companies can be irritatingly slow when providing you with a guarantee if you are an in-patient or out-patient, and you may find yourself having to pay cash/credit if you want to make it to the airport in time for your flight. Note that while there are CT-scans on the island, there's no MRI. For this you'll have to go to Bangkok or the mainland. The island's hospitals are each able to treat the vast majority of cases that they see. In more complicated cases, the patient is referred to hospitals outside the island and helicopter airlift service is available in extreme cases.
Dentists
Numerous dentists have established themselves on Samui and reflect the increasing role that health tourism plays. Dental care in Thailand is very reasonably priced and very good.
Pharmacies
Koh Samui has well over 100 pharmacies, most of which are English speaking. They can be found in most towns and villages except for the more internal remote mountain areas.