Over the past twenty five years the study of Thai dialects has concentrated on the geographical variation of either tones or lexical items. In the 1990s another type of Thai dialect study began to take shape- a combination of geographical and social variation study. Age has been identified as the main factor influencing variation in Thai dialects. The new type of study has so far concentrated on lexical variation. This paper deals with both geographical and social variation and both lexical and tonal variation. The Thai variety investigated in this study is that of that of Southern Thai spoken on Samui Island in Surat Thani province. The areas covered are the seven subdistricts of the Samui Island district. Two parallel studies were undertaken culminating in two M.A. theses. Research planning and data collection in these two studies were carried out jointly. Results show that there is no geographical variation in Samui Thai either in tonal or lexical usage. When considering social variation, however, this study confirms that age play a very important role. It clearly influences lexical variation in Samui Thai but it does not influence tonal variation. While the 60-70 years old speakers still use Southern Thai and Samui Thai lexical items and tones, the 10-20 year old speakers readily adopt Standard Thai lexical items but they still use the same tone system and tonal characteristics as the 60-70 years old speakers. It is suggested that future studies should investigate age-based tonal and lexical variation in Standard Thai and Thai dialects further to obtain a better picture of the process of ongoing change in Thai.