Large immigration flows of young Mexican women to the U.S.-Mexico border are increasing the demand for maternity services in the Southwest. To date no attempt has been made to determine how U.S. births are distributed among stable, permanent residents and transient migrants, such as border residents of Mexico who enter the U.S. temporarily, yet long enough to use health services. This exploratory study examines factors associated with childbirth in California by border residents of Tijuana, Mexico. Data on 184 women, 15-44 years old, who gave birth between 1982-87, were examined using a household survey and focus group discussions. The findings indicate that 10.4% of the sample crossed the border to give birth in the United States. Socio-economic and legal status, spoken English proficiency, history of U.S. residency, annual visits across the border, single parenthood and primiparity were factors significantly associated with childbirth in the United States. These factors, in addition to social class differentials in attitudes towards U.S. obstetrical care and citizenship-by-birth need to be examined in future studies of cross-border utilization of services. The findings also demonstrate that most U.S. deliveries were in the private sector and paid for out of pocket, representing a very low public health burden. Changes in Medicaid legislation, which have extended maternity care coverage to the undocumented, may encourage deliveries in the public sector. These effects, coupled with the bridging effects that newly legalized immigrant networks exert on friends and relatives, familiarizing them with U.S. health care resources, will require monitoring to determine changes in demand for U.S. maternity care by this population.