Abstract Context Correction of hyponatremia might represent an additional treatment for improving stroke patients’ clinical outcomes. Objective Admission hyponatremia is associated with worse clinical outcome in stroke patients, but whether normalization of hyponatremia improves outcome is unknown. We investigated whether normalization of hyponatremia affects patients’ disability, mortality, and stroke recurrence within 3 months; length of hospitalization; and discharge destination. Design This was a registry-based analysis of data collected between January 2016 and December 2018. We linked data from Swiss Stroke Registry (SSR) with electronic patients’ records for extracting sodium values. Setting We analyzed data of hospitalized patients treated at University Hospital of Basel. Patients Stroke patients whose data and informed consent were available. Main outcome measure Modified Rankin Scale (mRS) score at 3 months. The tested hypothesis was formulated after SSR data collection but before linkage with electronic patients’ records. Results Of 1995 patients, 144 (7.2%) had hyponatremia on admission; 102 (70.8%) reached normonatremia, and 42 (29.2%) remained hyponatremic at discharge. An increase of initial sodium was associated with better functional outcome at 3 months (odds ratio [OR] 0.94; 95% CI, 0.90-0.99, for a shift to higher mRS per 1 mmol/L sodium increase). Compared with normonatremic patients, patients who remained hyponatremic at discharge had a worse functional outcome at 3 months (odds ratio 2.46; 95% CI, 1.20-5.03, for a shift to higher mRS). No effect was found on mortality, recurrence, or length of hospitalization. Conclusions In hospitalized acute stroke patients, persistent hyponatremia is associated with worse functional outcome. Whether active correction of hyponatremia improves outcome remains to be determined in prospective studies.