In 1999, a survey was carried out in 1,008 Thai children aged 7 years, which found that 85 (8.5%) children were habitual snorers, and 7 (0.69%) children had mild obstructive sleep apnea syndrome (OSAS). Since the natural history of snoring and untreated mild OSAS is still largely unknown, this study was undertaken in 2002 in the same group of children to determine the natural history of snoring and OSAS. Questionnaires, consisting of questions about snoring, were sent to the parents of the 1,008 children. Polysomnography was performed in 1) the 7 children who had OSAS in the previous survey, and 2) other habitual snorers who had sleep-related symptoms in this survey. Seventy-five percent of the questionnaires were returned. The prevalence of habitual snoring had decreased slightly, from 8.5% in 1999 to 6.9% in 2002. Sixty-five percent of the children who had snored habitually in the previous survey no longer did so, whereas 4.5% of the children who previously never snored or snored sometimes had become habitual snorers. Of the 7 children who had OSAS previously, 5 had persistent snoring, and polysomnographic studies revealed more severe OSAS, with an apnea-hypopnea index (AHI) of 1.5-9.2 per hour of sleep. Five children were newly diagnosed with OSAS in this survey, with an AHI of 1.5-7.5. The overall prevalence of OSAS in this survey was 10/755 (1.3%). In conclusion, 65% of children who snored habitually no longer did so when they got older, while 9% of children had developed OSAS. We suggest that regular follow-up in children with habitual snoring may be needed, and additional research is required to determine the indications for polysomnography and neurobehavioral and cardiovascular assessment. We also showed that children with mild OSAS could develop more severe disease if left untreated, suggesting that deferment of treatment may have negative consequences.