Biliary atresia is the number one cause of cirrhosis and liver transplantation in children. Hyponatremia is the most important electrolytic disturbance observed in decompensated cirrhosis. Studies of hyponatremia in cirrhotic children are scarce and those that exist have defined hyponatremia as serum sodium < 130 mEq/L lasting for at least 7 days. We evaluated transplant-free survival (Kaplan-Meier) of children with cirrhosis due to biliary atresia and serum sodium < 130 mEq/L persisting for 1, 2-6, and ≥7 days. This was a single-center, historical cohort that included all patients aged ≤ 18 years on a liver transplantation waiting list. We studied 128 patients. The overall frequency of hyponatremia was 30.5% (39/128). Thirteen patients (10.2%) had hyponatremia when put on the list, and 20.3% developed it during follow-up. The Kaplan-Meier overall transplant-free survival rate was 83.3%. Patients with persistent hyponatremia for at least two days had the lowest transplant-free survival. Glomerular filtration rate (P = .00, RR = 0.96, IC 95% = 0.94-0.99), BMI/age Z-score (P = .02, RR = 0.59, IC 95% = 0.39-0.91), INR (P = .00, RR = 1.43, IC 95% = 1.17-1.74), and serum sodium (P = .04, RR = 0.91, IC 95% = 0.84-0.99) were independently associated with transplant-free survival. We did not observe any difference in mortality prediction after adding sodium to the original PELD score. We conclude that persistent hyponatremia lasting at least two days may herald poor prognosis for children with cirrhosis due to biliary atresia.