Background: Bariatric surgery has been proven the most effective treatment of morbid obesity, but micronutrient deficiency following bariatric surgery is a major concern. Increasing evidence points to a generally poor micronutrient status in obese subjects. Methods: We assessed micronutrient status in 232 morbidly obese subjects (BMI≥35 kg/m2) prior to bariatric surgery. Serum albumin, calcium, phosphate, magnesium, ferritin, hemoglobin, zinc, folate, vitamin B12, 25-OH vitamin D3, and intact parathormone (iPTH) were determined. In a sub-sample of 89 subjects, we additionally assessed copper, selenium, vitamin B1, B3, B6, A, and E levels. Results: Deficiencies were found in 12.5% of the subjects for albumin, 8.0% for phosphate, 4.7% for magnesium, 6.9% for ferritin, 6.9% for hemoglobin, 24.6% for zinc, 3.4% for folate, and 18.1% for vitamin B12. In addition, 25.4% showed a severe 25-OH vitamin D 3 deficiency, which was accompanied by a secondary hyperparathyroidism in 36.6% cases. Prevalence of albumin deficiency (p<0.007) and of anemia (p<0.003; in women only) significantly increased with BMI. Of note, 48.7% of the subjects showed at least one of the most prevalent deficiencies, i.e., vitamin B12, zinc and severe 25-OH vitamin D3 deficiency. In the sub-sample, 32.6% showed a selenium, 5.6% a vitamin B3, 2.2% a vitamin B6, and 2.2% a vitamin E deficiency. Copper, vitamin B1, and vitamin A deficiency was found in none of the subjects. Conclusion: Data indicate a high prevalence of micronutrient deficiencies in morbidly obese subjects. Based on these results, we strongly recommend a systematic assessment of the micronutrient status in all candidates for bariatric surgery.