The main focus of this descriptive study was to examine the incidence and duration of hypothermia in preterm infants at Prapokklao Hospital, Chantaburi. The study samples, selected by purposive sampling, were preterm infants who were admitted at the neonatal intensive care unit, during October, 1, 1997 to December, 31, 1997. The instruments used in the study were digital electronic thermometers and time clocks, validated and tested for reliability by the Physical Department, Faculty of Science, Chiang Mai University. The environmental thermometers and hygrometers were validated and tested for reliability by the North of Climatology. Data were collected by using demographic data recording forms, body temperature recording forms, environmental temperature and humidity recording forms, and procedure and treatment recording forms. These instruments were confirmed content validity by three experts. Data were collected by the researcher and five trained research assistants, and were analyzed using frequency, percentage, incidence of hypothermia, and the Mann - Whitney U test. The results showed the characteristics of the study samples as follows: gestational age was between 28 and 36 weeks with the mean of 33.7 weeks

birth weight varied from 800 to 3,200 grams, averaging 1,792.4 grams

and the Apgar scores at 1 minute and 5 minutes were two to ten, and eight to ten respectively. The incidence of hypothermia of the samples was found to be 86.0 percent. Nonetheless, this rate had increased up to 91.7 percent in the cases of referring from other health services. In addition, the rate tended to be increased in those who had low gestational age, birth weight, and Apgar score. The duration of hypothermia was between 30 and 510 minutes with the median of 120 minutes. Further, the factors found to be significantly influenced this duration included referring cases from other health services, birth weight less than or equal 1,500 grams, and nurturing in incubators. The findings indicated that it is necessary for health profession to develop a practical and effective guideline for caring and protecting hypothermia in preterm infants from the delivery room, through neonatal intensive care units.