Introduction: Diabetes mellitus (DM) is a chronic multisystemic disorders that causes complications that include long-term damage, dysfunction and failure of various organs in the body. Objective: The study aimed at determining the awareness of the chronic complication of DM that included ocular disorders, stroke, heart attack/heart failure, foot ulcer, skin rashes, sexual organs dysfunction and pregnancy losses by the subjects with DM at Onitsha, South Eastern Nigeria. Materials and Methods: This was a cross-sectional, descriptive hospital-based study involving 128 consenting DM subjects at St Charles Boromeo Specialist Hospital, Onitsha. The study-subjects were recruited using a convenient sampling method. Data collection was done with a pre-tested researcher-structured questionnaire. Laboratory tests that included fasting plasma glucose and glycated haemoglobin were done. Also, blood pressure and anthropometric measurements were done. Data was analysed using SPSS version 25. The mean values and the standard deviation of the continuous variables were calculated. Categorical variables were presented in tables as frequencies and percentages and compared using Chi-Square test. The level of significance was set at p ˂ 0.05. Result: A total of 128 DM subjects were studied comprising 98.4% type 2 DM subjects and 1.6% subjects with gestational DM respectively. The mean age of the subjects was 59.41 ± 12.32 years. 40.6% and 59.4% of the subjects were male and female subjects respectively. The most commonly known chronic complications of DM among the subjects were poor vision/blindness (87.5%), foot ulcer (75.0%), stroke (55.5%), renal failure (38.3%), heart attack/heart failure (35.9%) and skin rashes (26.6%) respectively. The least commonly known complications were sexual organ dysfunction (16.4%) and miscarriage/pregnancy loss (8.6%) respectively. The sources of information on the chronic complications of DM among the subjects included, friends/family members ...