Problem Preeclampsia is a major cause of fetal and maternal mortality and morbidity. Disturbed fetal-maternal immune tolerance, and therewith memory T cells, might be involved in its etiology. This study aims to give insight into memory T-cell populations and its associated cytokines in the decidual layers in early-onset preeclampsia (EO-PE) and late-onset preeclampsia (LO-PE). Method of Study Lymphocytes were isolated from the decidua parietalis and basalis from EO-PE (n = 6), LO-PE (n = 8) and healthy (n = 15) pregnancies. CD4(+)and CD8(+)central- (CCR7(+)), effector- (CCR7(-)), tissue resident- (CD103(+)), and regulatory- (Foxp3(+)) memory cell (CD45RO(+)) populations and their activation status (CD69(+)) were analyzed using flow cytometry. qRT-PCR analysis was performed on decidua parietalis and basalis biopsies to detect mRNA expression ofinterferon-gamma,interleukin-1B,IL2,IL6,IL7,IL8,IL10,IL15, andIL23. Results CD4(+)central-memory (CM) cell proportions were lower in the decidua parietalis in LO-PE (P < .0001) and EO-PE (P < .01) compared to healthy pregnancies. CD8(+)memory (P < .05) and CD8(+)CM (P < .01) cell proportions were also lower in the decidua parietalis in EO-PE compared to healthy pregnancies. This was accompanied by higherIL15(P < .05) andIL23(P < .05) and lowerIL7(P < .05) mRNA expression in decidua basalis biopsies from EO-PE compared to healthy pregnancies, analyzed by qPCR. Conclusion In conclusion, decidual memory T-cell proportions, their activation status, and associated cytokines are altered in preeclampsia and might therefore be involved in fetal-maternal immune tolerance and the pathophysiology of preeclampsia.