Purpose The impact of mild hyponatremia on geriatric syndromes is not clear. Our aim was to determine associations between mild hyponatremia and results of comprehensive geriatric assessment tools in outpatient settings. Methods We reviewed medical records of 1255 consecutive outpatient elderly subjects and compared results of comprehensive geriatric assessment measures among patients with mild hyponatremia (serum Na+ 130-135 mEq/L) versus normonatremia (serum Na+ 136-145 mEq/L). The comprehensive geriatric assessment measures included the Basic and Instrumental Activities of Daily Living, Mini Mental State Examination, Geriatric Depression Score, Tinetti Mobility Test, the Timed Up&Go Test, the Mini Nutritional Assessment, the handgrip test, the Insomnia Severity Index, polypharmacy, recurrent falls, urinary incontinence, orthostatic hypotension, and nocturia. Results Of the 1255 patients, 855 were female (68.1%), and the mean age was 73.7 +/- 8.3 years. Mild hyponatremia was detected in 108 patients (8.6%). The median serum sodium was 140.5 [interquartile range (IQR) 138.4-141.8] versus 133.8 [IQR, 132.3-134.2] in normonatremia and mild hyponatremia groups, respectively (p < 0.001). The only significant difference for comorbidities between normonatremia and mild hyponatremia groups was the frequency of hypertension (66.9% versus 76.7%, respectively (p = 0.041). None of the comprehensive geriatric assessment tools conferred a significant association with mild hyponatremia. Of the 1061 subjects with available survival data, 96 (9.0%) deceased within 3-4 years of follow-up (p = 0.742). Hyponatremia as an independent variable did not have a significant effect on mortality in univariate logistic regression analysis (OR 1.13, 95% CI 0.55-2.33, p = 0.742). Conclusion Mild hyponatremia does not apparently affect results of geriatric assessments significantly. Whether particular causes of hyponatremia may have different impacts should be tested in further studies.