Compliance with antipsychotic treatment is a well-recognized concern in the ongoing management of individuals with schizophrenia. The present investigation incorporated the Medication Event Monitoring System (MEMS) to evaluate compliance in a group of outpatients (N=52) with schizophrenia or schizoaffective disorder. Evaluating compliance as a dichotomous variable and using a threshold of 80%, the rate of noncompliance as measured by MEMS was 52%, considerably higher than self-report (3%), clinician rating (24%) and pill count (25%). The ability of treating clinicians to predict compliance/noncompliance was limited: 13 of 31 (42%) subjects they rated as compliant were noncompliant while 4 of 9 (44%) rated as noncompliant were actually compliant according to MEMS. Factors most consistently associated with noncompliance were higher total symptom scores and dosing complexity i.e., greater than once daily. Based on MEMS data, the overall mean level of compliance was 66%; however, it remains unclear as to what threshold is associated with a compromise in clinical response. More sophisticated measurement tools such as MEMS may assist us in better understanding how level and pattern of antipsychotic noncompliance, factors that at present remain poorly understood, impact on symptom exacerbation.