Aim: This study aimed to evaluate the association between Body Mass Index (BMI) and sympathetic nervous system function, as assessed by the Cold Pressor Test (CPT), in adult males. Material and Methods: A cross-sectional study was conducted on 100 male adults aged 18–45 years, categorized into three BMI groups: normal weight, overweight, and obese, based on WHO guidelines. Sympathetic function was evaluated using the CPT, where changes in systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) were measured in response to cold exposure. Participants with chronic illnesses, cardiovascular disorders, or medications affecting autonomic function were excluded. Data analysis involved ANOVA to compare sympathetic reactivity across BMI groups, with significance set at p < 0.05. Results: Sympathetic reactivity, as indicated by changes in SBP, DBP, and HR during CPT, was significantly higher in overweight and obese participants compared to those with normal BMI. Mean SBP changes were 10.2 ± 2.9 mmHg, 15.5 ± 4.2 mmHg, and 19.8 ± 4.7 mmHg for normal weight, overweight, and obese groups, respectively (p < 0.001). Similar trends were observed for DBP and HR, with all parameters showing statistically significant differences across BMI categories (p < 0.001). Conclusion: BMI is significantly associated with heightened sympathetic nervous system activity during acute stress. Individuals with higher BMI exhibit greater changes in SBP, DBP, and HR, suggesting a direct link between obesity and autonomic dysfunction. These findings emphasize the need for BMI management to mitigate the risks of obesity-related cardiovascular and metabolic disorders.