Objective: To study associations between serum ionised calcium, serum parathyroid hormone (PTH) and blood pressure. Design: A population based, cross-sectional study was used. Methods: Blood pressure, body mass index, serum ionised calcium and serum PTH were measured in 460 males and 486 females in the Tromsø study in 1994/1995. None were on medication for hypertension. The data were analysed with a multiple linear regression model. Results: When looking at subjects with serum ionised calcium <1.39 mmol/l, there was a significant negative association (P < 0.01) between serum ionised calcium and PTH. There was no association between blood pressure and serum ionised calcium. In both sexes there was a significant positive association between age and serum PTH (P < 0.01). For women, but not for men, there was a significant positive association between serum PTH and systolic and diastolic blood pressure (P < 0.01). Within each age group there was a difference in both systolic and diastolic blood pressure of 3-10 mm Hg between the upper and lower serum PTH halves of the female population. Females with hypertension had significantly higher serum PTH levels than the normotensive females (P < 0.01). Conclusion: Serum PTH is strongly and positively associated with blood pressure in women.