A term infant had a life-threatening inferior venal caval thrombosis d
uring the first 24 hours of life. The plasma from the infant and his m
other was found to be resistant to activated protein C and to be heter
ozygous for the factor V mutation (FV Leiden) associated with this dis
order, The presence of this hereditary disorder should be considered i
n infants with thrombosis and in infants with conditions predisposing
them to thrombosis.