Pregnancies of fourteen women who gave birth to babies with trisomy 13 were studied retrospectively for evidence of pre-eclampsia, with twenty-eight controls matched for age and parity. Of the five nulliparous women who subsequently gave birth to a baby with trisomy 13 all had had severe pre-eclampsia, compared with none of the control group. The records of eleven women whose first babies had had trisomy 18 (four) or trisomy 21 (seven) were also studied with appropriate controls and none of these pregnancies had been complicated by pre-eclampsia. Development of pre-eclampsia may be influenced by a gene or genes on fetal chromosome 13.