To examine residential mobility (i.e., moving) during pregnancy and in the first year of an infant's life using a large, prospective birth cohort in Rhode Island. Participants were recruited from Women and Infants Hospital of Rhode Island between January 5, 2009 and March 19, 2009. Residential histories were collected from mothers in-person immediately post-partum and by phone at 7 months and at 13 months post-partum. Of 1,040 mothers interviewed at birth, 71% (n = 740) completed the 13 month follow-up interview. Forty-one percent of mothers (n = 300) moved at least once between conception and 1 year post-partum, with the number of moves ranging from 0 to 8. Among movers, 69.0% moved once, 21.0% moved twice, and 10.0% moved three or more times. Mothers who moved tended to be younger, have fewer children, were not White, and had lower household incomes than those who did not move. Mothers who moved during pregnancy had 2.05 (95% CI: 1.40-2.98) times the odds of moving post-partum than mothers who had not moved in the antenatal period. There were statistical differences across socio-demographic groups with regard to when, where, and why mothers moved. Forty percent of movers during pregnancy (n = 61) moved for at least one negative reason, while 32.2% of movers during infancy (n = 64) relocated under negative circumstances. A substantial proportion of mothers moved pre- and post-partum, frequently under negative circumstances. Study findings have important implications for obstetric and pediatric providers who seek to understand, retain, and improve the health of their patient populations.