Background: Vitamin and mineral deficiencies are common after a sleeve gastrectomy (SG). The aim of this study is to examine the effectiveness of a specialized bariatric multivitamin (WLS Optimum) for SG patients on deficiencies compared with a regular multivitamin (MVS) for up to 5 years. Methods: Data of all patients who underwent a SG procedure in the Catharina Hospital Eindhoven (CZE) between July 2011 and July 2016 were collected and retrospectively analyzed. All patients who completed a preoperative blood test and at least one blood withdrawal during the first operative year were included in this study. Results: This study included 970 patients; 291 patients in the WLS-user group and 679 patients in the non-WLS-user group. In favor of the user group, significantly less de novo deficiencies were found of vitamin B1 (2 years) and vitamin B6 (two and three), folic acid (1 and 2 years), and vitamin B12 (at 1 year). Binomial logistic regression showed a significant influence of multivitamin supplementation mainly on ferritin; vitamins B1, B6, B12, and D; and folic acid, (all p < 0.05). The total number of de novo deficiencies was significantly reduced during the whole study for all WLS Optimum users. Conclusions: Vitamin deficiencies are common, and postoperative nutritional management after SG is underestimated. The use of a specialized multivitamin supplement resulted in higher mean serum concentrations and less deficiencies of vitamin B1, folic acid, and vitamin B12. This study shows that SG patients benefit from the specialized multivitamin supplements, but adjustments are required for iron and vitamin B6 content.