Morbidity estimates of conditions originating in the perinatal period have not been reported in the United States. Conditions originating in the perinatal period were identified according to the International Classification of Diseases. The National Hospital Discharge Survey provided a weighted, nationally representative sample of newborns discharged each year from short-stay, nonfederal hospitals. From 1986 through 1987, 33.7% of all newborns had at least one nonteratologic perinatal condition. However, 6.8% of all newborns had physiologic jaundice as their only discharge diagnosis. Nonphysiologic jaundice was diagnosed in 4.4%, maternal causes of perinatal morbidity in 3.1%, birth trauma in 2.5%, fetal distress in 2.3%, birth asphyxia in 2.1%, and infections specific to the perinatal period in 2.0% of all newborn discharges. The average hospital stay for all newborns was 3.5 days, but it was 5.3 days for newborns with at least one nonteratologic perinatal condition and 2.6 for newborns discharged without a morbid condition. This study provides nationally representative estimates of perinatal morbidity useful for comparisons with smaller hospital-based samples. In addition, the study provides estimates of the public health impact of these conditions in terms of hospital stay days.