If you arrive in Thailand by air you will pass through the customs area as you leave the airport. Use the green channel if you have nothing to declare but it unsure use the red channel and speak to a customs officer. If you enter Thailand by rail, customs officers will board the train to carry out their duties. Customs formalities are straightforward, and the officers are polite and efficient.
You are allowed to bring in 200 cigarettes or 250 gr. of tobacco, 1 litre of spirits, plus a reasonable amount of perfume. If you are bringing in prescription drugs ask your doctor for a note detailing the drugs you are taking.
Fire-arms, pornography and narcotics are strictly prohibited, and the penalties for drug trafficking are severe.
Antiques may only be taken out of Thailand with a certificate from the Fine Arts Department in Bangkok. A reputable dealer will be able to offer advice on the practicality of obtaining this certificate. Buddha statues old or otherwise, may not be taken out of the country. (This does not apply to the very small items found in gift shops).