The present study evaluated consistency, reliability, and determinants of two real-world measures of adherence to prescription in 57 schizophrenia and 61 non-schizophrenia patients. Treatment resistant schizophrenia (TRS) was additionally diagnosed in 28 of the schizophrenia patients. Patients were screened for clinical severity, cognitive functioning, and adherence by 10-item Drug Attitude Inventory (DAI-10) or Adherence-to Therapy (AtT), a clinician-rated tool developed by our group. DAI-10 and AtT scores showed a significant correlation (p=0.039; rho=0.21; df=103). Compared to the DAI-10 scale, a higher number of variables were associated with AtT. In schizophrenia and TRS patients, substance abuse was the only significant predictor of lower DAI-10 score (p=0.027, F=5.2, R-2=0.07, and p=0.06, F=8.9, R-2=0.23, respectively). Lower AtT score was significantly associated with first-generation antipsychotic use (p=0.001, RR: 2.00 [1.40-2.87]), positive symptoms (p=0.02, RR: 1.63 [1.05-2.53]), impaired verbal fluency (p=0.01, RR: 1.88 [0.81-4.32]) or problem solving (p=0.01, RR: 2.14 [0.92-4.98]). AtT, but not DAI-10, score correlated with the score on the Personal and Social Performance scale (p=0.02, F=5.86, R-2=0.08). Overall, AtT score was predicted by pharmacological, psychopathological, and cognitive factors, and predictive of psychosocial functioning. Therefore, AtT measure may represent a convenient and practical tool to evaluate schizophrenia patients' adherence.