OBJECTIVE The aim of this study was to evaluate maternal and fetal serum levels of homocysteine, folic acid, vitamin B12 and placental tissue levels of homocysteine and their association with severity of pre-eclampsia. METHODS A case-control study, performed by a single center, included 26 pregnant women with mild pre-eclampsia, 26 pregnant women with severe pre-eclampsia and 26 healthy pregnant women. Maternal blood was collected before delivery and fetal blood was collected from the umbilical cord at delivery. Placental tissue samples were obtained after delivery of placenta. Homocysteine, folic acid, vitamin B12 levels in serum and homocysteine levels in placental tissue homogenates were analyzed by immunochemiluminescent assay. RESULTS Homocysteine levels in both maternal and fetal serum were significantly higher in the severe pre-eclampsia group compared to mild pre-eclampsia and control groups. However, homocysteine levels in both maternal and fetal serum were not significantly different between mild pre-eclampsia and control groups. No significant differences were observed in folic acid and vitamin B12 levels in both maternal and fetal serum between the groups. Homocysteine levels in placental tissue homogenates were too low to be measured in the three groups (<2 µmol/l). CONCLUSIONS Maternal and fetal serum homocysteine levels were found to be significantly higher in severe pre-eclampsia group compared to mild pre-eclampsia and control groups suggesting that elevated serum levels of homocysteine might be associated with severity of pre-eclampsia. On the other hand it seems like elevated serum homocysteine levels were not associated with deficiency of folic acid and vitamin B12.