Purpose: This study was performed to compare the clinical findings and identify differences in risk factors between early-onset preeclampsia (EO-PE) and late-onset preeclampsia (LO-PE). Materials and Methods: This retrospective study included 516 women with singleton pregnancies and preeclampsia (none of them had superimposed preeclampsia on chronic hypertension) who delivered in a tertiary care center. Clinical findings, and maternal and perinatal outcomes were compared between early (< 34 weeks’ gestation) and late (≥ 34 weeks’ gestation) onset of the disease. Results: Incidences of nulliparity, previous preterm births, stillbirths, and first trimester abortions were significantly higher in women with EO-PE (p < 0.05). History of disease other than chronic hypertension (especially diabetes mellitus) and previous term births were significantly higher in women with late-onset disease (p < 0.05). The mean gestational week at delivery and mean birth weight were significantly lower in early-onset disease (p < 0.05). Stillbirths, early and late neonatal deaths, and cases where the mother’s life at risk were significantly higher in women with early-onset disease (p < 0.05). Conclusions: EO-PE appears to be mediated by the placenta and associated with higher incidence of perinatal, neonatal and maternal deaths, and maternal nearmiss cases.