Introduction: Sleeve gastrectomy (SG), which was first described as a part of the duodenal switch procedure, has become the most commonly used type of metabolic surgery in Turkey and the world. This study is an evaluation of the effects of SG surgery on the levels of glucose metabolism, liver enzymes, and thyroid hormones in the first postoperative month, according to age and gender. Materials and Methods: A total of 124 consecutive patients who underwent SG at a single center between January 2018 and September 2019 were retrospectively evaluated for enrollment. The biochemical parameters of the patients measured at the first postoperative month were evaluated and any differences between female and male patients were analyzed. Results: Twenty-five patients were excluded from the study due to insufficient data and the study was performed using the records of 99 patients. Of the group, 70 (70.7%) were female and 29 (29.3%) were male, with a mean age of 35.42±11.47 years (range: 18-68 years). Preoperative alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyl transferase (GGT) values were found to be significantly higher in male patients (p<0.05). No significant difference was observed between the male and female patients in terms of free-T4 and thyroid-stimulating hormone values, (p>0.05) whereas there was a significant difference between the genders in terms of free-T3 (fT3) thyroid hormone (p<0.05). There was no significant difference between the female and male patients in terms of glucose, glycated hemoglobin (HbA1c), or age. Conclusion: SG was found not only to have mechanical effects but also to cause many metabolic changes. There are currently too few studies in the literature examining how these metabolic changes alter the biochemical parameters. According to the results of a small number of studies, SG significantly reduces body mass index, and the levels of AST, triglycerides, and HbA1c. The results of this study indicated that AST, ALT, GGT, and fT3 levels were higher in men after SG than in women.