Aims: In women with Marfan syndrome pregnancy presents an increased risk of dilatation, dissection, and rupture of the aorta. The aim of this study was to investigate the influence of pregnancy on growth of the aortic root. Methods and results: Between 1993 and 2004 127 women with Marfan syndrome were prospectively followed; 61 women had one or more children; in 23 women, 33 pregnancies could be followed prospectively for aortic dimensions. Only one woman had suffered an aortic complication, a type A dissection (limited to the ascending aorta), before pregnancy. Out of 66 childless women a comparison group of 22 women was selected and individually matched. Mean initial aortic root diameter just before pregnancy was 37 ± 5 mm (range 25-45). Before, during, and after pregnancy the overall individual aortic root diameter change (in 31 pregnancies) was not significant (P = 0.77). Only the woman with a previous type A dissection developed an aortic complication (type B dissection) during her second pregnancy. No cardiac complications occurred in the other 22 women during their pregnancies. During a median follow-up of 6.4 years, no significant difference in growth of the aortic root was observed between the pregnancy group and the matched childless group (0.28 vs. 0.19 mm/year, P = 0.08, respectively). Conclusion: Pregnancy in women with Marfan syndrome seems to be relatively safe up to an aortic root diameter of 45 mm, at least as far as our observed diameter range of 25-45 mm is concerned.