Objective To assess in an animal model the effect of maternal dietary calcium intake during pregnancy on the blood pressure of offspring. Design Randomised controlled trial.Sample Ninety-eight 20-week-old female Wistar-Kyoto rats, giving birth to a total of 119 pups that were included in the follow up study. Methods Rats were randomised to a calcium deficient diet, a diet with the recommended calcium levels, or a diet with calcium content much higher than the recommended levels. After one month on the experimental diet they were bred. After birth, systolic blood pressure in the offspring was measured monthly till 52 weeks of age. Main outcome measures Blood pressure of the offspring.Results The difference in blood pressure of the offspring between the normal and low maternal calcium group increased 0.49 mmHg per month (95% CI 0.18 to 0.84), 0.38 (0.07 to 0.68) between the low and high calcium group, and 0.12 (À0.20 to 0.43) between the normal and high calcium group. At the end of the follow up (52 weeks of age) blood pressure of the offspring in the deficient calcium group was 12.1 mmHg (95% CI 8.8 to 15.4, P < 0.0001) higher than in the normal calcium group and 7.5 mmHg (95% CI 4.4 to 10.5, P < 0.001) higher than the high calcium group. Blood pressure of the offspring in the high calcium group was 4.3 mmHg (95% CI 1.0 to 7.5, P ¼ 0.01) higher than in the normal calcium group. In a multiple regression model maternal calcium intake during pregnancy was the strongest predictor of blood pressure of the offspring during adulthood. Conclusions This experiment supports previous studies in humans suggesting a link between calcium intake during pregnancy and blood pressure in the offspring, and provides an animal model to explore the mechanisms involved in such association.