This study evaluated reasons for nonadherence in a random 10% sample of the patients identified as nonadherent (PDC less than 80%) from the study below. We found that 40% of patients classified as nonadherent were misclassified, with 31% of those due to external fills, and 60% due to provider-recommended gaps in therapy. Most cases of true nonadherence were due to an inability to reach the patient.