The urinary sodium/potassium (Na/K) ratio was evaluated in 220 children aged 3-16 years living in Cimitile, a small town near Naples in Southern Italy by utilizing 24 hour urinary collections. The Na/K ratio averaged 3.79 +/- 1.68 and correlated significantly (p less than 0.001) with age, body weight and height but not with Body Mass Index (BMI). No difference was seen when data were analyzed by sex. Mean daily sodium excretion averaged 3.91 +/- 1.52 mM/Kg while potassium excretion averaged 1.17 +/- 0.54 mM.Kg. The Na/K ratio was higher than that observed in children studied in Israel, United Kingdom, USA, and the Federal Republic of Germany and is of the same magnitude of that previously reported in children born in Japan. This high Na/K ratio is a case for concern because of the risks connected with high Na/K ratio in urine.