Information on the relationship of neighborhood characteristics to objective indicators of dietary intake is extremely limited. The aim of this observational cross-sectional study was to examine the association between neighborhood socioeconomic status (SES) and 24-hour urinary excretion of sodium and potassium in a population with a high ratio of urinary sodium to potassium. Subjects were 1,032 female Japanese dietetics students aged 18 to 22 years, residing in 293 municipalities in Japan. Neighborhood SES index was defined by seven municipal-level variables, namely unemployment, household overcrowding, poverty, education, income, home ownership, and vulnerable groups, with an increasing index signifying increasing neighborhood socioeconomic disadvantage. Urinary excretion of sodium and potassium was estimated from a single 24-hour urine sample. Neighborhood SES index was not significantly associated with 24-hour urinary excretion of sodium (mean value for each quartile of neighborhood SES: 133.5, 135.2, 126.5, and 141.7 mmol/day, respectively; P for trend 0.10) or potassium (mean value for each quartile: 43.5, 42.2, 38.4, and 42.5 mmol/day, respectively; P for trend 0.44). However, neighborhood SES index was significantly positively associated with the ratio of 24-hour urinary sodium to potassium (mean value for each quartile: 3.14, 3.28, 3.37, and 3.41, respectively; P for trend 0.03). This significant association remained after adjustment for household SES variables (mean value for each quartile: 3.15, 3.35, 3.29, and 3.41, respectively; P for trend 0.04). Neighborhood socioeconomic disadvantage was associated with higher ratio of 24-hour urinary sodium to potassium in young Japanese women.