Health and Safety
Malaria and dengue fever are rare but not unheard of in Thailand's southeast. Health authorities have done a great job controlling mosquitoes around the southern resorts, but you'll still need a good supply of repellent. Wear long-sleeve shirts and long pants at dusk to reduce the chances of dengue.
As with any developed resort locations, the dangers and annoyances usually involve petty theft. Phuket has its fair share of crime, usually thefts from hotel rooms or pickpockets operating in the entertainment areas. Ensure that your valuables are secured at all times. Brawls caused by too much liquor and sun can also be a problem. There are many bars and pubs here, and some tend to overindulge. The police do patrol the area, but violence does occasionally break out.
Be careful at the beach, as the sun is stronger than you think. Wear a hat and plenty of sunscreen. Protective clothing while diving or snorkeling is a good idea, as accidentally brushing against or stepping on coral can be painful. Keep an eye out for dangerous creatures like jellyfish, especially during the monsoon season, and sea urchins. If you are stung, seek medical attention immediately.
Strong undertows often develop during monsoon season, especially along the west coast. Pay attention to posted warnings and listen if locals tell you not to swim.