The aim of this study was to identify the features of first episode schizophrenia that predict adherence antipsychotic medication at six-month follow-up. We used validated instruments to assess clinical and socio-demographic variables in all patients with first episode schizophrenia from a defined geographical area admitted to a Dublin psychiatric hospital over a four-year period (N=100). At six-month follow-up (N=60) we assessed adherence to medication using the Compliance Interview. One third of patients with schizophrenia were non-adherent with medication within six months of their first episode of illness. High levels of positive symptoms at baseline, lack of insight at baseline, alcohol misuse at baseline and previous drug misuse predict non-adherence. These results indicate that an identifiable subgroup of patients with first episode schizophrenia is at high risk of early non-adherence to medication. While high positive symptom scores pre-date and predict non-adherence in most patients, reduced insight is the best predictor of non-adherence in patients who do not misuse alcohol or other drugs.