ObjectivesTo assess the magnitude of internalised stigma and associated factors among patients with bipolar disorder attending the outpatient department of Amanuel Mental Specialized Hospital, Addis Ababa, Ethiopia.DesignInstitution-based cross-sectional study design.SettingAmanuel Mental Specialized Hospital, Addis Ababa, Ethiopia.ParticipantsWe recruited about 418 participants using systematic sampling technique for an interview during the study period.MeasurementData were collected by face-to-face interviews. Internalized Stigma of Mental Illness scale was used to measure internalised stigma. The Rosenberg Self-Esteem Scale and the Oslo-3 Social Support were instruments used to assess the associated factors. Bivariate and multivariate logistic regressions were performed to identify factors associated with the outcome variable. ORs with 95% CI were computed to determine the level of significance.ResultsThe magnitude of internalised stigma was 24.9% (95% CI: 21.2% to 28.9%). In the multivariate analysis, unemployed (adjusted OR (AOR)=2.3, 95% CI: 1.0 to 5.0), unable to read and write (AOR=3.3, 95% CI: 1.05 to 10.7), poor social support (AOR=5.3, 95% CI: 1.9 to 15.0), ≥4 previous hospitalisations due to bipolar disorder (AOR=2.6, 95% CI: 1.1 to 6.1) and low self-esteem (AOR=2.4, 95% CI: 1.1 to 5.1) had a significant association with internalised stigma.ConclusionsOne in four patients with bipolar disorder reported high internalised stigma. Unemployment, low educational status, low self-esteem, poor social support and being hospitalised more than three times before were significantly associated with internalised stigma. Thus, a stigma-reduction programme focusing on self-esteem improvement and psychological health of patients to increase their stigma resistance to counteracting effects of internalised stigma is essential.