Variation in 24-h blood pressure (BP) is associated with multiple factors, but the association has not been thoroughly examined in young adults. To elucidate the potential factors associated with variation in 24-h BP, 331 healthy medical students were investigated. Awake mean BP negatively correlated with sleep duration in males. Sixty-seven subjects (20.2%) had a high 24-h BP according to the ESH/ESC 2007 guidelines (systolic blood pressure (SBP) 125 and/or diastolic blood pressure (DBP) 80 mmHg). After multivariate analysis for confounding factors, male gender, body mass index (BMI), smoking, the 24-h low/high frequency component (heart rate variability spectral analysis), and short sleep (5 h or less) were found to be associated with high BP. The present study is the first to demonstrate the multivariate risk factors for elevated 24-h BP in a large number of young adults. Further investigation is required to determine the causal relationship between modifiable BP-related factors and elevated 24-h BP in young adults.