Two cases of reversible posterior leukoencephalopathy syndrome (RPLS) are reported. One was a 26-year-old woman, who had pre-eclampsia and developed cortical blindness and subsequent eclampsia at 28 weeks' gestation. The other was a 27-year-old woman, who had no pre-eclampsia and developed loss of consciousness and subsequent systemic convulsion at 36 weeks' gestation. On brain magnetic resonance imaging, they both had high signal intensity on T2-weighted and fluid-attenuated inversion recovery images, and normal signal intensity on diffusion-weighted image of the posterior lobe, which almost disappeared with the amelioration of clinical symptoms thereafter. RPLS is considered to be the result of vasogenic brain edema caused by hypertension. Two hypotheses are conceived to explain the emergence of RPLS without hypertension. The first suggests that an immunotolerant condition such as pregnancy can easily cause vasogenic edema without the elevation of blood pressure. The second suggests that hypertension exists but cannot be detected because it is extremely acute and transient.