The purpose of this study was to investigate the clinical characteristics and assess other factors associated with geographic tongue in Thailand. One hundred and eighty-eight Thais with geographic tongue and 188 controls were interviewed regarding their medical history, symptoms, and the nature and migratory pattern of their lesions. Variations in the clinical appearance, lesion location, and any associated tongue fissures were recorded. The age range for the 188 subjects was 9 to 79 years. The highest incidence (39.4%) occurred in the 20-29 age group. Women were affected more than men (1.5:1). The leading group of medical conditions consisted of allergy-related disorders; however, the incidence of these problems among both subjects and controls was not significantly different (55.2% vs. 44.8%). Our results demonstrated a significant co-existence of geographic tongue and fissured tongue. Most of the geographic tongue lesions manifested a typical appearance consisting of a central atrophic area bounded by a raised white circinate line (69.1%) with multiple tongue sites affected (62.8%). The most common locations were at the lateral margins and tip of the tongue. The majority of our subjects (75.5%) were asymptomatic. The results of this study correspond with the findings of previous geographic tongue studies in other populations.