This study aims to assess the prevalence of preoperative and postoperative nutritional deficiencies and associated factors in patients who are eligible for laparoscopic sleeve gastrectomy. Patients who underwent primary laparoscopic sleeve gastrectomy between December 2018 and April 2020 were included in the study. All patients were screened by detailed laboratory tests pre- and post-laparoscopic sleeve gastrectomy 6th and 12th months. Patients' data, which were recorded prospectively, were analyzed retrospectively. A total of 228 patients were included in the study. The mean age was 39 ± 11.5 (60% female), and the mean body mass index was 41.2 ± 6.3 kg/m2. In the preoperative period, anemia was detected in 20 female patients (9%), low ferritin levels were detected in 25%, B12 and folic acid deficiencies were detected in 2.6% and 12.3%, respectively, and vitamin D deficiency was detected in 76% of the patients. During the postoperative follow-up, 77% of the patients received multivitamin supplements regularly. Mean body mass index regressed to 27.1 ± 4.2 kg/m2 in the first year. Incidence of anemia was found at 4.8%, low ferritin levels were 14%, folate deficiency was 5.3%, B12 deficiency was 5.3%, and vitamin D deficiency was 25% in the 12th month. Vitamin A, zinc, biotin, and thiamine deficiencies were 8.8%, 6.6%, 11%, and 2.2% in the 12th month, respectively. In the preoperative period, we detected significant deficiencies in some vitamins. The incidence of de novo vitamin deficiency during post-laparoscopic sleeve gastrectomy follow-up was low. Regular multivitamin-multimineral use may have an effect on this.