Intra-individual variability in blood pressure is well recognized but its determinants have been largely unexplored. In a recent cross-sectional study, 343 subjects from a male working population were assessed. Ten supine blood pressure readings were taken at 2-min intervals for 20 min on each of three consecutive days. Each subject's body mass index (weight/height2) was recorded and a questionnaire completed to record demographic details and information about physical activity, personality characteristics, dietary habits, tea and coffee consumption, smoking habits and alcohol consumption. When systolic and diastolic blood pressure variability was defined as the average coefficient of variation of the 10 readings each day, systolic blood pressure variability was found to be positively correlated with alcohol consumption, verbal aggression score and extroversion score. Diastolic variability was positively correlated with verbal aggression score, type-A personality score and extroversion score, and negatively associated with age. Stepwise regression analysis revealed alcohol consumption to be the strongest determinant of systolic variability while age was the strongest determinant of diastolic variability. We conclude that alcohol consumption, age and personality characteristics may be important determinants of intra-subject variability in blood pressure.