Background: Hypertension is associated with elevated sodium and low potassium intakes. The determination of sodium and potassium intake by dietary records is inaccurate, being its measurement from 24-hour urine collection the reference method. Aim: To determine urinary sodium and potassium excretion in adults. To compare dietary sodium and potassium intake and their excretion from an isolated urine sample against the reference method. Material and methods: Seventy healthy adults aged 35 ± 8 years with a body mass index 25±2 kg/m2 (36 women) were studied. Urine was collected over 24 hours, including an isolated urine sample taken in fasting conditions. Additionally, three 24-h dietary records were performed. Results: Reported sodium and potassium intake was 2720±567 and 1068±433 mg/day, respectively. In turn, urinary excretion of sodium and potassium was 4770±1532 and 1852±559 mg/day, respectively. These latter values were significantly higher than those obtained by dietary records. Furthermore, the urinary sodium and potassium excretion estimated from an isolated urine sample was 4839±1355 and 1845±494 mg/day, respectively. These values were similar to those obtained with a 24 h urine collection. Conclusions: Dietary records underestimated electrolyte intake when compared with the reference method. Using an isolated urine sample to estimate electrolyte intake may be a reliable alternative.Background: Hypertension is associated with elevated sodium and low potassium intakes. The determination of sodium and potassium intake by dietary records is inaccurate, being its measurement from 24-hour urine collection the reference method. Aim: To determine urinary sodium and potassium excretion in adults. To compare dietary sodium and potassium intake and their excretion from an isolated urine sample against the reference method. Material and methods: Seventy healthy adults aged 35 ± 8 years with a body mass index 25±2 kg/m2 (36 women) were studied. Urine was collected over 24 hours, including an isolated urine sample taken in fasting conditions. Additionally, three 24-h dietary records were performed. Results: Reported sodium and potassium intake was 2720±567 and 1068±433 mg/day, respectively. In turn, urinary excretion of sodium and potassium was 4770±1532 and 1852±559 mg/day, respectively. These latter values were significantly higher than those obtained by dietary records. Furthermore, the urinary sodium and potassium excretion estimated from an isolated urine sample was 4839±1355 and 1845±494 mg/day, respectively. These values were similar to those obtained with a 24 h urine collection. Conclusions: Dietary records underestimated electrolyte intake when compared with the reference method. Using an isolated urine sample to estimate electrolyte intake may be a reliable alternative.