Background: Preeclampsia is a unique idiopathic syndrome in human pregnancy that can involve almost all organ systems. Objectives: The aim of the present study was to compare the periodontal diseases between the preeclamptic and normal pregnant women in order to find a possible risk factor relationship. Materials and Methods: This case-control study was performed on 200 pregnant women, with maternal age ≤ 35 years and gestational age ˃ 20 weeks with singleton pregnancies. Of these, 100 women were preeclamptic with proteinuria and blood pressure ≥ 140/90 and 100 women with normal blood pressure in the control group. Oral examination was performed on all women by a dentist for detection of periodontal diseases. Gingivitis and periodontitis were diagnosed based on the American Academy of Periodontology (AAP)/American Dental Association (ADA) classification, using the measurement method of Ramfjord. The preeclamptic women were then sub-classified into mild and moderate and comparisons were made between all groups. Results: The mean maternal age, BMI, neonatal birth weights and gestational age at delivery were not significantly different between the preeclamptic and normal groups. There was a significant association between preeclampsia and periodontal diseases (P ˂ 0.01). The mean number of involved teeth (P ˂ 0.001) and the mean pocket depth (P = 0.04) were higher among the preeclamptic group. Gingivitis was more frequent among the cases with mild (56.8%) compared to (31.6%) in the severe preeclamptic group (P = 0.04). Periodontitis was more prevalent among the cases with severe preeclampsia which was not statistically significant. The mean neonatal birth weight was significantly lower in the group with severe preeclampsia (P < 0.01). Conclusions: There was a significant association between preeclampsia and periodontal diseases. The number of involved teeth and pocket depth were higher among the preeclamptic mothers compared to normal pregnant women.