To assess how reliably hospitals report serious, uncommon communicable diseases to the Department for Public Health, we searched the 1995 hospital discharge data set (HDDS) collected by the Kentucky Health Policy Board for cases of 11 diseases. Of 17 case records found, 4 represented disease occurrences that had been reported to the Department; 6 represented coding errors in the HDDS; 4 were instances where a reportable disease had been suspected but not confirmed by subsequent workup; 1 case was a resident of another state; and 2 were cases of invasive Hemophilus influenzae infection in adults that should have been reported to the Department. The study found no evidence that hospitals failed to report vaccine-preventable diseases. There was evidence that the HDDS needs improved accuracy to maximize its usefulness for public health purposes.