Decrease in intraocular pressure (IOP) during pregnancy has been reported by previous studies, but these studies have concentrated on the last trimester of pregnancy or one reading per trimester. Moreover, IOP changes during pregnancy in ocular hypertensive subjects have never been described. Therefore, the present study was planned to determine IOP throughout the pregnancy, in both normal and ocular hypertensive subjects. Intraocular pressure was measured at six-week intervals throughout the pregnancy in 44 normal and 32 ocular hypertensive women. Intraocular pressure was also measured in 44 normal and 32 ocular hypertensive non-pregnant controls of the same age group. IOP measurements were taken with the Goldmann applanation tonometer. In normal subjects, IOP decreased significantly at the 18th week (p < 0.05). The IOP differences between first and second (p < 0.05) and second and third (p < 0.01) trimesters of pregnancy were significant. In these subjects, pregnancy decreased IOP by 19.6%. About 35% of total decrease occurred between 12th and 18th weeks of pregnancy. In ocular hypertensive subjects, IOP decreased significantly at the 24th week (p < 0.05). The IOP differences between second and third (p < 0.001) trimesters of pregnancy were significant. In these subjects, pregnancy decreased IOP by 24.4%. About 61% of total decrease occurred between 24th and 30th weeks of pregnancy. In both groups, decreases in IOP were independent of systolic and diastolic blood pressures, body weight, height, and number of previous pregnancies. With advancing pregnancy, intraocular pressure decreases. The higher decrease in ocular hypertensive subjects may be due to their higher level of ocular pressure. In ocular hypertensive subjects, pregnancy can decrease intraocular pressure up to a level of normal limit.