The potentially preventable readmission (PPR) method uses administrative data to identify hospital readmissions that may indicate problems with quality of care. The PPR logic determines whether the reason for readmission is clinically related to a prior admission, and therefore potentially preventable. The likelihood of a PPR was found to be dependent on severity of illness, extremes of age, and the presence of mental health diagnoses. Analyses using PPRs show that readmission rates increase with increasing severity of illness and increasing time between admission and readmission, vary by the type of prior admission, and are stable within hospitals over time.