In a clinical prospective 3-year study of 158 children aged 2 weeks to 14 years with hypernatraemic dehydration (serum sodium 150 mmol/l or more), infants predominated (61.4%). The 158 children with hypernatraemia accounted for 13.7% of all children admitted with gastroenteritis over the same period, and significant aetiological factors included the use of artificial feeds, differences between the children with hypernatraemia and those with normo- or hyponatraemia, P < 0.001, P < 0.001, respectively; the use of breast milk, P < 0.001, P < 0.001, respectively; nutritional status, P < 0.001, P < 0.001, respectively; and clinical state of mild to moderate dehydration P < 0.001; P < 0.001, respectively; but not with patients considered severely dehydrated. There was also a significant difference between the presence of neurological features in hyper- and normonatraemic patients P < 0.001; in hyper- and hyponatraemic patients P < 0.05, and in mortality rate between hyper- and normonatraemic patients, P < 0.05 but not between hyper- and hyponatraemic patients. A history of refusal to feed or vomiting was obtained in 41 children (25.9%). The mean serum sodium was 155.5 mmol/l (range 150-189 mmol/l); mean serum urea 7.7 mmol/l (range 1-18.9 mmol/l). Hypernatraemic dehydration remains an important and serious complication of childhood gastroenteritis in our area of study. The use of artificial milk feeds is contributory, and well-nourished babies appear more at risk. We recommend more liberal water intake during gastroenteritis and the public should also be educated on and made more aware of this condition.