BackgroundDiabetes mellitus is a progressive disease that compromises the quality of life of the victims. Patients’ knowledge about diabetes mellitus self-care is vital in achieving targeted glycemic control and minimizing complications of the disease. However, there are limited studies in Ethiopia on the subject to guide interventions. Hence, this paper aimed to assess knowledge about diabetic self-care and complications among diabetes mellitus patients in Addis Ababa, Ethiopia.MethodsAn institutional-based cross-sectional study design was employed. A structured questionnaire was used to assess knowledge; participants who responded correctly to at least 6 of the eight questions were classified as having good knowledge about the complications and those who answered <6 questions correctly were classified as having poor knowledge. Participants who correctly responded to ≥30 of the 37 self-care questions were classified as having good knowledge about diabetes self-care; those who correctly responded to <30 questions were classified as having poor knowledge. Multivariate logistic regression analyses were used to identify associated factors.ResultOverall, 202 (51.7%) of the study participants had good knowledge about the complications, and 279 (71.4%) of the participants had a good knowledge of self-care. Receiving diabetic education was a significant modifiable factor for having poor knowledge about both the complication (AOR= 3.078(1.323,7.160)) and the self-care (AOR=7.645(3.153,18.538)).ConclusionAbout half (51.7%) of the participants had good knowledge about the complications, and about three in four (71.4%) had good knowledge about self-care. Receiving diabetic education was significantly associated with both complication and self-care knowledge status. Focusing on the quality and quantity of the information that is delivered to diabetes mellitus patients can improve the quality of care and the outcome.