To study long-term nutritional deficits based on adherence to a standardized nutritional care after gastric bypass (GBP). Long-term prospective data on nutritional complications after GBP are missing. It is not known whether severe deficiencies are prevented by standard multivitamin supplementation and what parameters are influenced by patient adherence to nutritional care. One hundred forty-four consecutive subjects from our prospective database (90% women, initial body mass index: 48 ± 15 kg/m2, age: 43 ± 10 years) who underwent GBP more than 3 years before the study were assessed. Multivitamins were systematically prescribed after GBP, and additional supplements were introduced if deficiencies were recorded during follow-up. We identified a group of 66 compliant subjects who attended yearly medical visits and a group of 32 noncompliant subjects who were recalled because they had not attended any visit for more than 2 years. Weight loss was 42 ± 14 kg at 3 years or later. The number of nutritional deficits per subject was 3.2 ± 2.3 before surgery and did not significantly increase between 1 and 3 years or later after GBP (3.4 ± 2.0 and 3.5 ± 2.3, respectively). However, specific nutritional deficits occurred despite long-term multivitamin supplementation, including vitamins B1, B12, and D and iron. Noncompliant subjects had more deficits than compliant subjects (4.2 ± 1.9 vs 2.9 ± 2.0 deficits per patient, P < 0.01) and the number of deficits correlated with the time from last visit (r = 0.285, P < 0.01). Lifelong medical care is required to maintain a good nutritional status after GBP. Monitoring of nutritional parameters is necessary to add supplementation for deficits that are not prevented by multivitamin preparations.