OBJECTIVE: The aim of this study was to assess sociodemographic and clinical correlates of poor treatment adherence among outpatients with bipolar disorder (BD) in remission period. METHODS: This was a cross-sectional study carried out in a University Hospital in Turkey, and 117 outpatients with BD according to DSM-IV-TR criteria were included. All participants were administered a sociodemographic form, the SCID-I, the Morisky 8-item Medication Adherence Questionnaire, the Hamilton Depression Scale, the Young Mania Rating Scale, Schedule for Assessing the three components of insight, and Global Assessment of Functioning Scale. Collected data were analysed via descriptive statistics and logistic regression was used to determine significant variables. RESULTS: Patients with poor treatment adherence were low educated, were more likely to be not married, and had a greater prevalence of anxiety disorder comorbidity. The patients with poor adherence also showed more subsyndromal depressive symptoms but no significant differences were seen in terms of age, gender, living status, social support, or number of episodes between patients with good and poor adherence. Logistic regression analyses revealed that comorbid anxiety disorder, lower education level, and duration of depression period were the main predictors of poor adherence. CONCLUSION: This outcome is consistent with previous studies, and assuring complete adherence in all bipolar patients is difficult, but increasing the number of adherent patients is possible and substantial for sufficient outcome. Improving subsyndromal symptoms and awareness of the patient about the features of the disorder may provide better adherence to treatment and greater functionality of the patient. Psychotherapeutic interventions and psychoeducation should be implemented along with the medical treatment to improve subsyndromal symptoms and to avoid treatment maladherence in advance. Further research is needed to assess the role of interventions in treatment adherence of patients with BD.