The combination of the mother’s exact birth date along with the mother’s first name and either the father’s last name or mother’s maiden name gave a conclusive match for 94.1 percent of the matched sample of women. The exact date of mother’s birth, along with a partial name match, accounted for a further 2.7 percent of matches. Partial name matches and either an address match (0.5 percent) or a transposed date of mother’s birth year, month, or day segment (2.7 percent) accounted for the remaining matches. During this matching process, the Washington Dental Service data manager received infants’ birth dates only from the birth certificate data manager, and the birth certificate data manager did not receive dental utilization data from Washington Dental Service. All successful matches combined with infants’ birth dates (n 5 29,215) were sent back to Washington Dental Service, where it was determined whether eligibility for dental services existed during a period 40 weeks prior to birth and for how many months eligibility existed. Prior to 1995, eligibility for dental services could be determined only for those women who had at least one dental visit, whereas subsequent to 1995 eligibility could be determined regardless of whether a dental visit occurred. This change in method of determining eligibility did not impact the reported findings