Immunization information systems (IISs) are confidential, population-based systems that contain immunization data for children, and, in some cases, adults, within a geographic area. There are generally two models for participation in an IIS, termed voluntary exclusion or "opt-out" and voluntary inclusion or "opt-in." Using the Texas opt-in consent system and statewide IIS (ImmTrac), we describe the costs associated with obtaining opt-in consent in hospitals as part of the birth registration process and in provider offices for children without prior consent. We also estimate the costs associated with a hypothetical opt-out system. Between October 2006 and August 2007, project staff conducted on-site time studies for patients in 8 birthing hospitals (n = 281), 16 provider offices (n = 131), and ImmTrac state offices in Austin, Texas (n = 100). Total costs per child and costs per year were estimated using a time-and-motion study in which the time associated with discussing ImmTrac and obtaining ImmTrac consent was measured. The annual costs associated with obtaining consent for Texas' opt-in IIS are estimated at $1 389 804.61. The average per child cost associated with ImmTrac consent completed at birth is $2.00, whereas the per child cost for consent completed in provider offices is $2.64. The annual costs of operating an alternative, opt-out system are estimated at $110 714.03, or $0.29 per child. This cost analysis demonstrated that the proposed opt-out costs were substantially less than the actual opt-in model currently utilized. Changing to an opt-out system could redirect limited healthcare funding to more critical areas such as vaccine purchasing and administration.