© 2016 Elsevier B.V.Background: Research on antipsychotic medication non-adherence in first-episode psychosis patients tends to examine non-adherence behaviors and attitudes together. Nonetheless, attitudes do not always directly translate into behaviors. We examined the baseline predictors for antipsychotics non-adherence behaviors and attitudes separately in a first-episode psychosis cohort. We also included cognitive impairments as one of the predictor variables as this domain is rarely explored in adherence studies. Method: Participants were 313 adult-onset psychosis patients recruited from the Jockey Club Early Psychosis project in Hong Kong. Demographic, premorbid, clinical, and cognitive characteristics were first assessed at baseline. Six months later, participants completed a 14-item Medication Compliance Questionnaire, which was a modified and Cantonese-translated version of the Medication Adherence Rating Scale that includes items pertaining to both adherence behaviors and attitudes. Results: Rates of poor adherence behaviors and negative adherence attitudes were 17.6% and 27.8%, respectively. Determinants of poor adherence behavior included more severe positive symptoms, hospitalization at onset of illness, and poorer engagement in extended social network. As for negative adherence attitude, determinants included more severe general psychopathology, poorer insight, more psychic medication side-effects, and poorer performance on backward digit span test and WAIS-R information test. Conclusions: The risk factors for non-adherence behaviors and attitudes are different and they should all be taken into careful consideration while formulating appropriate intervention programs to tackle the adherence problem in adult onset psychosis. ; Link_to_subscribed_fulltext