OBJECTIVE To examine the effect of chronic hypertension (CH), with and without superimposed pre-eclampsia (PE), on the incidence of a small-for-gestational-age (SGA) neonate and to explore the possible mechanism for such association. METHODS Data for this study were derived from prospective screening for adverse pregnancy outcomes in women with singleton pregnancy attending their first routine hospital visit at 11-13 weeks' gestation, which included recording of maternal characteristics and medical history and measurement of mean arterial pressure (MAP). Birth-weight Z-score, adjusted for gestational age and maternal and pregnancy characteristics, and incidence of SGA were compared between those with and those without CH in the total population and in the subgroups of pregnancies with and without PE. Regression analysis was used to examine the relationship between MAP and birth-weight Z-score and incidence of SGA and PE in those with and those without CH. RESULTS The study population constituted 74 226 pregnancies, including 1052 (1.4%) with CH and 73 174 without CH. PE developed in 233 (22.1%) cases of the group with CH and in 1662 (2.3%) of those without CH. In the group that developed PE, there was no significant difference for either median birth-weight Z-score or incidence of SGA between those with CH and those without CH. In the group without PE, the incidence of SGA was twice as high in those with CH than in those without. There was a significant association between log10 MAP multiples of the median and incidence of SGA and PE, which was more marked in those with CH than in those without. CONCLUSIONS CH is associated with an increased risk of SGA and PE and this is related to MAP at 11-13 weeks' gestation. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.