Visa on arrival is typically 15-30 days (most visitors from Western countries receive 30 days) and Visa extensions can be applied if necessary. Tourists can also apply for a non-immigrant Visa for medical reasons, which gives them 90 days and requires proof that they’re receiving treatment from a licensed medical facility. In addition, starting from early 2013, medical tourists from GCC countries including Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and The United Arab Emirates can enter Thailand for 90 days without visa.
Please note that you cannot enter Thailand for medical reasons under “Visa exemption rule”. The Visa must be obtained before leaving your homeland. However, it is not a problem to stay in Thailand as a tourist after treatment, provided the validity on the Visa still remains