Consanguineous union increases the risk of genetic disorders in offspring. The present study aimed to evaluate the prevalence and characteristics of parental consanguinity in Hong Kong, and its effects on pregnancy, perinatal, and child health outcomes. Pregnant women in consanguineous unions attending an obstetrics unit at a public hospital in Hong Kong were retrospectively studied. Their pregnancy, perinatal, and child health outcomes were compared with an ethnicity-matched control group of pregnant women in non-consanguineous unions. The overall prevalence of parental consanguinity was 0.6% (first cousins or closer, 78.4%; beyond first cousins, 21.6%). The majority were ethnic Pakistani (85.0%). Women in consanguineous unions were more likely to have an obstetric history of congenital abnormality (10.5%), unexplained intrauterine fetal demise (4.2%) and unexplained neonatal death (4.6%), or family history of congenital abnormality (4.6%). Offspring of consanguineous parents had significantly higher risk of recessive diseases (odds ratio [OR]=8.70, 95% confidence interval [CI]=1.06-71.36), structural abnormalities (OR=4.55, 95% CI=2.17-9.53) and developmental delay (OR=6.72, 95% CI=1.48-30.63), and significantly higher incidence of autistic spectrum disorder (2.1%; P=0.008). It is essential that information on the increased risks associated with parental consanguinity is included in genetic counselling for consanguineous couples, so that they can make informed decisions.