Nationwide surveillance of Rh hemolytic disease of the newborn (RhHDN) indicates that, after a substantial decline in incidence, reported rates reached a plateau in the late 1970s. We conducted a study designed to validate RhHDN surveillance data, to obtain corrected incidence estimates, and to identify potential reasons for the reported plateau. We obtained data from the Birth Defects Monitoring Program, a national surveillance system that collects data from public and private hospitals participating voluntarily. We asked hospitals for copies of the medical records for all infants discharged with a code for RhHDN and for a sample of the medical records of infants discharged with a code for other and unspecified hemolytic disease during 1986. The estimated incidence rate of RhHDN was 10.6 per 10 000 total births, with some regional variations. Our findings indicate that, despite the availability of an effective preventive measure, RhHDN continues to contribute significantly to infant morbidity and mortality in the United States.