The association between small for gestational age (SGA) birth at term and inter-pregnancy interval was examined in a hospital cohort of 4489 multiparous women. The greatest risk of SGA birth was found in women with the shortest inter-pregnancy intervals. Even after adjusting for multiple confounding factors, women whose inter-pregnancy interval was 18 or fewer months (over one-third of women in the cohort) remained at twice the risk of giving birth to a term SGA infant when compared with women whose inter-pregnancy interval was 24-36 months. In a logistic regression analysis examining the occurrence of SGA birth in women with inter-pregnancy intervals of 36 months or less, a strong linear association was noted between these two factors. The association of term SGA birth with short inter-pregnancy interval could result from one or more physiologic factors that might act to limit fetal growth. In that case, short inter-pregnancy interval would represent a potentially preventable cause of SGA birth.