Obesity has increased enormously in the past decades and is associated with many comorbidities and a decreased life expectancy. One of the most efficient weight loss treatments for obese people is bariatric surgery. But a long-term success can only be ensured through adequate aftercare. Therefore, the aim of our ABARO-Study was to examine the aftercare, complaints, weight development, and quality of life of patients even several years after bariatric surgery to develop recommendations for adequate aftercare in a further step. The present analyses were based on a linked data set comprising longitudinal health claims data and cross-sectional data from a patient survey. Patients with a bariatric intervention between 2004 and 2018 were identified and invited to fill in the survey, comprising sociodemographic and medical data, information about complaints, aftercare, lifestyle information, and psychometric scales. The BMI respectively the excess weight loss were calculated for the time immediately after surgery and when filling out the survey. A lot of the study participants suffered above all from fatigue, diarrhea, reflux, and flatulence even several years after surgery, and a lot of them reported a dumping syndrome. We found strong associations between the quality of aftercare and the weight development as well as with the quality of life and psychological stress. Our findings suggest that the aftercare is an important factor to ensure long-term success of the treatment after bariatric surgery. With regard to these findings, optimization of aftercare is absolutely necessary, refering not only to the postoperative consultations in the bariatric surgery centers but also to the long-term and holistic aftercare provided by general practitioners, gastroenterologists, nutritionists, psychologists—and also dermatologists and orthopedists.