The National Incidence (NI) study estimated how many cases of child abuse and neglect were known to professionals in the United States from May 1979 through April 1980. The study used a stratified random sample of 26 counties within 10 States so as to represent all counties in the Nation. Data on child abuse were obtained from child protective services agencies and from other agencies likely to have contact with child abuse cases. The NI study failed to measure child sexual abuse incidence, since there is probably less 'new' data on sexual abuse than on other abuse forms, because so many of the NI cases were officially reported cases, i.e., cases known only to professionals. Also, the study limited its definition of sexual abuse only to cases where the child's caretaker was the perpetrator, which is a more restrictive definition of child sexual abuse than that used in many treatment programs. The study is flawed in other aspects of perpetrator variables, particularly regarding female perpetrators, and it reports victims' ages at the time of disclosure rather than at the onset of abuse. The classification of sex acts should have been more expansive and detailed. Suggestions for future studies focus on a more inclusive type of incidence, the sexual abuse definition, and the kinds of data gathered. 17 references.