Pre-eclampsia is a major cause of maternal and foetal morbidity and mortality but the etiology and pathogenesis are basically unknown. Pre-eclampsia is clearly associated to the placenta (trophoblast) alone. Epidemiological observations have raised one of the most popular hypotheses of the genesis of pre-eclampsia--an immune maladaptation between mother and foetus. Markedly raised incidences are seen in blood relatives (mothers, sisters, daughters) to pre-eclamptic women. In the genetic studies, the importance of specific combinations of mother-foetus-genotypes are recognized. The pathological processes involve an aberrant trophoblast-invasion of the spiral arteries, placental dysfunction, abnormal levels of cytokines and endothelial cell dysfunction, resulting in systemic and organ dysfunction. Genetic linkage studies and the use of molecular biology will probably elucidate the predisposing factors, etiology and pathogenesis of pre-eclampsia in more detail. There might be several pathways ending up with the same clinical manifestations.