The association of underutilization of drugs prescribed for the treatment of hypertension and acute-care hospital readmissions was evaluated. The data base consisted of computerized hospitalization records and computerized out-patient pharmacy records, checked by chart audit for validity. The number of days' supply of antihypertensive agents was estimated by dividing the quantity of drugs dispensed by the daily dose indicated by the prescription instructions. All patients had been admitted to an acute-care hospital during a 6-month period with the diagnosis of hypertension. Following discharge from the hospital, drug utilization and readmission status were determined for a minimum of 1 year. The drug compliance of a group of patients who were readmitted to the hospital was compared with the patients who were not readmitted. The readmitted group had a significantly higher ratio of days when they were without any antihypertensive agents relative to the length of time in the study. There were no statistically significant differences in demographic features or blood-pressure levels between the patient groups. These findings indicate that underutilization of antihypertensive drugs may be associated with hospitalization, which could be prevented if patients had complied with their medication schedules.