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Hyponatremia (serum sodium concentration [Na+] < 136 mEq/L) is a potentially life-threatening condition. Recent evidence (Renneboog, Musch, Vandemergel, Manto, & Decaux, 2006) shows that even mild hyponatremia is associated with disorders of balance/gait. This retrospective analysis explored the influence of serum [Na+] on neuropsychological (NP) measurements at baseline from 44 patients with chronic hyponatremia who participated in an efficacy and safety study of an experimental compound over a decade ago. Group mean serum [Na+] was 124.8 ± 4.9 mEq/L. Age-adjusted partial correlations were computed between serum [Na+] and NP measurements, 39% of which were statistically significant--all involving psychomotor functioning. These findings replicate and extend previous observations that psychomotor deficits are, at least in part, associated with hyponatremia in these patients. While chronic hyponatremia is known to have deleterious effects on quality of life, motor and gait disturbances represent manifestations of mild hyponatremia that have until now gone unrecognized. A new class of medication, vasopressin antagonists, has been shown to correct hyponatremia. It will be important to explore the effects of correcting hyponatremia on psychomotor functioning in individuals with hyponatremia.