Introduction: some research studies have proposed that the alterations in serum potassium concentrations may contribute to the onset of hypertension and renal disorders described in pregnancy-induced hypertension syndrome. Objective: to compare serum potassium concentrations in preeclamptic and normotensive pregnant women. Materials and methods: this was a case-control study conducted in pregnant women attending Hospital Central “Dr. Urquinaona”, Maracaibo, Venezuela, between January 2014 and June 2021. A case group of patients diagnosed with preeclampsia (group A), as well as a control group including pregnant women with similar maternal age and body mass index to the study group (group B), were recruited into the study. Demographic characteristics, laboratory parameters and serum potassium concentrations were analyzed. Results: a total number of 515 pregnant women were included, of which 257 were assigned to group A and 258 to group B. Those in group A presented lower serum potassium concentrations than those in group B (p < 0.0001), whose values were only correlated with serum creatinine values in the case group (p = 0.023). No significant correlations were found with blood pressure values (p = ns). Conclusion: there are significantly reduced potassium concentrations in preeclamptics, compared to normal pregnant women.