Locate some common sense and bring it with you when vacationing anywhere in the Caribbean. Here...
MosquitoesRecently, St. Martin as well as several other Caribbean islands have been plagued with Chikungunya Virus. It is similar to Dengue Fever, and has no known cure. It has been spreading throughout the world recently, and was first recorded in the Western Hemisphere on St. Martin in January 2014. The government recommends long sleeves and using mosquito repellent high in DEET.
SunYou can burn within a remarkably short time; use sunscreen or block frequently depending on how long you're exposed. Do not fail to reapply it as recommended depending on where you are e.g., swimming, on boat, beach walking, with special attention to feet and backs of knees and neck. Brimmed hats and umbrellas can offer further protection.
CrimeThough the island is generally a safe place, like everywhere else in the world there is crime, and you should be aware of your surroundings at all times. Obviously you should lock your doors, avoid unpopulated areas and do not flash your money and jewelry around. Remember that this is a foreign country, and act accordingly. Tourists report many instances of parked rental cars being rifled. Organized teams can break in effortlessly. Best advice: Leave nothing of value in them at any time.
DrinkingBe aware that drinking is practically a national pastime in St. Maarten, and it is relatively easy and inexpensive to obtain alcoholic beverages $1.25 ice cold Heineken's are available almost everywhere including McDonalds and gas stations and therefore extremely easy to over-do it. Driving while impaired on the island is very risky as there are many places where you could end up in the ocean or down the side of a cliff. When in doubt, call a cab.
DrugsLike most places, drugs are readily available for those interested, but despite what someone may tell you Marijuana is not legal and certainly is not regulated as in certain parts of the Netherlands.
ParkingTake care in Philipsburg...there is very little parking and the tow zone areas are very poorly marked. If the spot is free and you think it shouldn't be then it is probably a tow area.
Jet blastIf you're on Maho Bay, watch out for approaching and departing planes. Get too close and a jet engine from a plane taking off can blast a lot of air, sand, or water into your face, or worse cause serious injury or death.
GLBT travellersIf you are GLBT be careful of your surroundings, as with many Caribbean islands the local culture doesn't have the same level of acceptance found in other countries. While not a large problem, each year there are reports of attacks based on sexual orientation. If you are considerate of your environment you won't have a problem but it should be noted that public displays of affection by GLBT individuals especially on the Dutch side may not be well tolerated.
Pharmaciesare denoted by a cross symbol, usually in neon and there are Hospitals with ambulance service on both sides of the island.
Dutch and French are the official languages on their respective sides of the island. The EU variety of English is an official language of the Dutch side as well and is widely spoken on both sides, especially in tourist areas. Children on both sides of the island are educated in French, Dutch, English and Spanish so language is typically not a barrier when visiting the island.
Generally, you'll find no dress codes for most places on St. Martin. Some high-end restaurants and night clubs do have some, though, so find out beforehand to avoid any disappointment.
St. Martin has a great deal of cultural diversity, and true locals are far outnumbered by immigrants from poorer and less urbane areas. Dressing too in too risqué a fashion can give the impression that you are looking for a "good time" and attract unwanted attention.
You may also offend some locals if you wander around in places other than the beaches and pools in your swimsuit: e.g., in your local supermarket as well as here, it's disrespectful and you may be treated accordingly.