Labor-onset hypertension is a poorly documented category, and there is scanty information concerning the outcome of pregnancy in this condition. A retrospective study was performed to compare the pregnancy outcome of 36 patients with labor-onset hypertension (group A) with 36 patients with classical preeclampsia diagnosed before labor (group B) who were matched for parity and age. There was no difference in age, past history of hypertensive pregnancies or family history of hypertension between the two groups. The need for intrapartum hypertensive and anticonvulsant treatment as well as the outcome of pregnancy were similar in both groups. The only significant difference was that group A patients had lower maximum and booking systolic and diastolic pressures. The results indicate that labor-onset hypertension represents a late manifestation of the preeclampsia process, because these patients had lower blood pressure in pregnancy and would not be identified until intrapartum elevation of blood pressure satisfied the diagnostic criteria of preeclampsia.