| Background: Obstructive sleep apnea syndrome (OSAS) is a chronic sleep-related breathing disorder associated with recurrent upper airway obstruction, intermittent hypoxia, cardiovascular dysfunction, metabolic abnormalities, and impaired quality of life. Tonsillar hypertrophy is an important anatomical factor contributing to airway obstruction in selected adult patients. Although tonsillectomy is considered an effective surgical treatment in such cases, evidence regarding its long-term cardiovascular and metabolic benefits remains limited. Aim: To evaluate the long-term effects of tonsillectomy on cardiovascular parameters, lipid profile, and sleep-related outcomes in adults diagnosed with obstructive sleep apnea syndrome after 3–5 years of follow-up. Materials and Methods: This retrospective observational study was conducted at the Department of ENT, at a tertiary care hospital, Al Ahsa City, Saudi Arabia. Adult patients diagnosed with OSAS who underwent tonsillectomy between January 2015 and December 2019 were included. Clinical records, biochemical investigations, and polysomnographic findings were retrospectively reviewed. Parameters including systolic blood pressure (SBP), diastolic blood pressure (DBP), lipid profile, Epworth Sleepiness Scale (ESS), apnea-hypopnea index (AHI), and oxygen saturation levels were compared preoperatively and postoperatively after 3–5 years of follow-up. Statistical analysis was performed using paired t-test, with p<0.05 considered statistically significant. Results: A total of 46 patients were included in the final analysis. The mean age of the patients was 42.3 ± 8.7 years, with male predominance (65.2%). Significant postoperative improvement was observed in cardiovascular parameters. Mean systolic blood pressure decreased from 143.1 ± 10.8 mmHg to 131.9 ± 8.9 mmHg, while mean diastolic blood pressure decreased from 91.7 ± 6.9 mmHg to 84.3 ± 6.1 mmHg (p<0.001). Significant improvement was also observed in lipid profile parameters, including reductions in total cholesterol, triglycerides, and LDL cholesterol levels, along with an increase in HDL cholesterol. Sleep-related outcomes improved markedly after surgery. Mean ESS score decreased from 16.1 ± 3.4 to 7.5 ± 2.6, and mean AHI improved from 33.4 ± 9.2 events/hour to 14.6 ± 6.2 events/hour (p<0.001). Lowest oxygen saturation levels during sleep also improved significantly following tonsillectomy. Conclusion: Tonsillectomy in adults with obstructive sleep apnea syndrome and significant tonsillar hypertrophy was associated with substantial long-term improvement in cardiovascular, metabolic, and sleep-related outcomes after 3–5 years of follow-up. Surgical intervention may represent an effective therapeutic option in carefully selected adult OSAS patients, particularly those with anatomical upper airway obstruction and poor tolerance to CPAP therapy.