Colorado's Child Support Improvement Project shows that in- hospital paternity interventions can produce dramatic increases in the voluntary paternity acknowledgement rate. Following the introduction of in-hospital paternity overtures to unmarried parents in four hospitals in Denver in 1993 and 1994, voluntary acknowledgement rates doubled or came close to doubling in each hospital. These significant increases resulted from project- inspired simplifications of the voluntary acknowledgement procedure, which have since been incorporated into State statute. Among the most significant changes were the elimination of fees and waiting periods associated with the voluntary acknowledgement procedure and the replacement of notarized signatures with witnessed ones. All unmarried parents were systematically approached, the benefits of paternity were explained, and interested parents were assisted in adding the father's name to the birth certificate. Voluntary paternity acknowledgement was confidential; no paternity information was directly communicated to the child support agency. Also, the increase in hospital paternity acknowledgement rates reflected efforts by project staff to train hospital personnel on paternity procedures, the development and distribution of videos and brochures to hospitals and appropriate prenatal care facilities, and the monitoring of hospital performance with the use of quarterly data extracts from the automated birth record reporting system. Voluntary paternity acknowledgement remains most attractive to the most financially independent elements of the unmarried population. It is unclear what must be done to attract more voluntary acknowledgement by the population that receives Aid for Families of Dependent Children or is at risk for needing such aid. Future demonstration projects should explore the impact of various policy initiatives such as employment and training programs for unmarried fathers and a Child Support Assurance System for unmarried mothers on voluntary acknowledgement rates.