Objective:To compare physician-reported adherence of specific patients to oral second-generation antipsychotics vs. actual adherence rates determined from the patients’ pharmacy claims.Methods:Claims data from the HealthCore Integrated Research Database identified patients with schizophrenia or bipolar disorder with ≥1 oral second-generation antipsychotic prescription. The prescribing physicians were identified from the pharmacy claims and asked to complete an Internet survey assessing their perception of medication adherence for 1–2 of their patients and their beliefs regarding adherence to second-generation antipsychotics in general for a 1-year period. Adherence to second-generation antipsychotics was determined for each patient by pharmacy claims for the same period. Physician survey data were merged with patient claims data via unique patient identifiers, and physician-reported adherence rates were compared with claims-based rates as measured by the medication possession ratio.Results:One hundred and fifty-three physicians responded to the survey, representing 214 patients (44 with claims for schizophrenia, 162 with bipolar disorder, 8 with claims for bipolar disorder and schizophrenia). Most physicians (60%) had no formal adherence training. More than two-thirds (68%) reported emphasising the importance of adherence and reported approximately 76% of their patients were adherent (≥71% of the time). In the schizophrenia group, 16 of 17 (94%) patients with low-to-moderate (≤70%) adherence levels had high (≥71%) physician-estimated adherence. In the bipolar disorder group, 62 of 92 (67%) patients with low-to-moderate adherence levels had high physician-estimated adherence.Conclusions/Interpretation:These analyses suggest that, even when physicians are asked about specific patients in their practice, there is discordance between physician perceptions and adherence as measured through pharmacy claims. This disparity may delay appropriate interventions, potentially contributing to relapses.