The present study represents an attempt to evaluate a systematic underestimation in reported mental hospital readmission rates. The case search of the medical records of 1137 admissions to the Cleveland Psychiatric Institute in 1957 resulted in discovery of 221 readmissions erroneously classified as first admissions. Corrections for this error elevated the reported crude readmission rate from 31.40% to 50.84%. Since the reported rate is roughly equivalent to nationally rates, and since the corrected rate is well above national averages (including those for Prolonged Care Hospitals and those for more recent years where higher rates are to be expected), the data suggest that a systematic reporting error may be widespread.Abstract Teaser