The use of contraceptives has become prevalent among females in Thailand in the past 20 years, and oral contraceptive use has been suggested to trigger changes in fat intake, energy expenditure, fat metabolism and blood pressure. Based on field investigations of 391 married women aged 20 years or over in Yasothon Province, North-east Thailand, this study aims to elucidate the effects of oral contraceptive use on body mass index (BMI: kg/m2 ) and blood pressure, taking into account reproductive histories and socioeconomic conditions. The proportion of obese (BMI> 25) subjects was high in the age groups 30–39, 40–49 and 50–59, accounting for, respectively, 39·4%, 51·1% and 48·5% of these populations. The proportion of women with hypertension (90/140 mmHg) was 23·7%, 18·5% and 26·2% in the 40–49, 50–59 and 60–69 age groups. Current contraceptive practices in the studied population included sterilization by operation, oral contraception and injection. These methods accounted for 43·0%, 12·8% and 8·2% of the population, respectively. Sociodemographic factors such as reproductive history, years of education and household income were not significantly related to BMI or to blood pressure (ANOVA with age adjustment). In contrast, oral contraceptive users had significantly higher BMIs and diastolic blood pressures (p<0·01, ANOVA with age adjustment). Multiple regression analysis also revealed that oral contraceptive use was a weak but significant contributing factor to both high BMI and blood pressure when sociodemographic factors were taken into account and controlled for statistically. It can thus be concluded that the use of contraceptive pills, which contain oestrogen and progestin and are provided free of charge to Thai women, tend to increase BMI and to elevate blood pressure.