Of 1045 children admitted with gastroenteritis over a 12-month period and studied retrospectively, serum sodium level was tested in 802. Sixty patients (7.5%) had hypernatremic dehydration (HD). The peak incidence of HD, the highest serum sodium levels, and the worst outcome were all encountered in infants under the age of 3 months. An association with pre-admission high solute feeding was less obvious. Pre-admission volume intake could not be evaluated. There was no association of HD with the etiological pathogen or climatic conditions. The weight-for-age was below the fifth percentile in 21 patients (35%). One patient (1.7%) died, another (1.7%) developed peripheral gangrene, and four (6.7%) were left with significant neurologic complications. All of these patients were under the age of 4 months. In this subtropical country, the most important risk factor for the development of hypernatremia in the course of gastroenteritis is the young age. Environmental risk factors do not seem to play a significant role.