Onset of severe hyponatremia following cisplatin (CDDP) administration has been previously reported. However, the risk factors associated with hyponatremia still remain unclear. We conducted a retrospective, single-center, case-control study to identify independent risk factors of severe hyponatremia in patients with various types of cancers. Adult patients who received intravenous CDDP administration between January 2012 and December 2017 met the inclusion criteria. The investigators recorded patients’ demographics and clinical information retrospectively, and assessed the lowest serum sodium level within 21 d of the first CDDP administration. Risk factors for grade ≥3 hyponatremia were examined via a logistic regression analysis. Among a total of 472 patients, fifty patients (10.6%) developed grade ≥3 hyponatremia. Univariate analysis revealed that age (≥65 years), presence of small cell lung or esophageal cancer, and lower sodium concentrations in the serum (<138 mEq/L) were significantly associated with grade 3 and 4 hyponatremia. Additionally, multivariable logistic regression analysis showed that the presence of small cell lung cancer (adjusted odds ratio, 3.26; 95% confidence interval (CI), 1.07–10.00) and lower sodium concentrations in the serum (<138 mEq/L) (adjusted odds ratio, 6.18; 95%CI, 3.21–11.90) were independent risk factors of grade 3 and 4 hyponatremia. Thus, serum sodium concentrations in patients with these risk factors should be closely monitored after CDDP administration.