Abstract: Introduction: Behcet's disease (BD) is a multisystem disorder with potential ability to influence pregnancy outcome. Changes in the BD may also occur during pregnancy. This study was designed to find the effect of pregnancy on BD and the outcome of pregnancy. Materials & Methods: We analyzed 59 pregnancies in 54 women with BD. The disease activity during pregnancy and in the 6 month period both before pregnancy and after delivery were calculated by the Physician Global Assessment (PGA) and the Iran Behcet's Disease Dynamic Activity Measure (IBDDAM). Changes in the disease activity were compared by chi square test. Pregnancy outcome and newborn status were determined. Results: The mean age of the patients at pregnancy was 27.8+4.5 with a mean disease duration of 5.6+3.7 years. The GPA showed no change in the disease activity in 47% of the patients during pregnancy. The disease exacerbated in 34% and improved in 19% of them. The IBDDAM showed the same results, although it was different in 3 patients (5%). After delivery the disease was stable in 43%, improved in 31% and aggravated in 26% of the patients. We have encountered 10 abortions, 1 premature labor and 1 stillbirth. There was no significant difference in the disease manifestations between patients with and without abortions, except for the eye involvement (p<0.002) especially anterior uveitis (p<0.005) and posterior uveitis (p<0.02). We had 47 full term pregnancies (80%). The newborns were all healthy except one who died due to neonatal sepsis. Conclusion: The effect of pregnancy on BD seems to be variable (no effect an the disease activity in half of the cases). IBDDAM can be a reliable index to evaluate disease activity during pregnancy with a sensitivity of 95%. Reminding a 20% rate of pregnancy failure in BD patients, there is major concern about the outcome of pregnancy in these patients. This would be more important in the casts with eye involvement.