Objective: Diabetes mellitus is also known as the "silent killer" if the symptoms are neglected, and complications are found. Diabetes mellitus is one of the four non-communicable diseases causing 60 % of deaths--and the prevalence of diabetes mellitus complications in South Sulawesi is 32.71 %. This study aimed to examine the risks of obesity, duration of diabetes, physical activity, smoking habits, and hypertension for complications in patients with diabetes mellitus. Methods: This study is analytical observational with a case-control study design, in which data were collected from 150 patients with diabetes mellitus in Makassar, selected by purposive sampling with 50 respondents in the case group and 100 respondents in the control group, respectively. Data were collected using a questionnaire and the relationship between research variables was analyzed using the Odds Ratio and multiple logistic regression. Results: The results showed that obesity status (OR = 2.346; 95 % CI: 1.172-4.696), duration of diabetes (OR = 9.793; 95 % CI: 4.328-22.159), and hypertension status (OR = 2.455; 95 % CI: 1.218-4.948) are risk factors for complications in patients with diabetes mellitus. Meanwhile, physical activity (OR = 1.282; 95 % CI: 0.644-2554) and smoking habits (OR = 1.882; 95 % CI: 0.871-4.066) are not risk factors. The logistic regression test showed that the duration of diabetes is the variable most at risk for diabetes mellitus complications with a magnitude of risk of 10.123 times greater. Conclusion: It is expected that patients with diabetes mellitus will pay attention to the condition of their bodies, especially in controlling blood sugar levels, managing their diet, and maintaining blood pressure to prevent complications.