Inclusion Criteria:  Aged 18 and more Scheduled for an elective, laparoscopic bariatric surgery (either laparoscopic gastric sleeve resection or laparoscopic gastric bypass) BMI > 30 kg/m2 moderate to high risk for PONV (defined as APFEL score of 2 or higher) Informed Consent as documented by signature (see appendix 2).  Exclusion Criteria:  emergency or open abdominal surgery;  contraindication to aprepitant:  known allergy/hypersensitivity on pimozide, terfenadine, astemizole or cisapride  on regular medication with known interaction with the study drug:  benzodiazepines ketoconazole, itraconazole rifampicin, clarithromycin paroxetine diltiazem carbamazepine, phenytoin tolbutamid ritonavir St. John's wort patients with history of chronic nausea/vomiting or taking medication with known antiemetic properties (dexamethasone, metoclopramide, meclozine) severe hepatic impairment (Child-Pugh score >9); chronic substance abuse (except smoking); significant psychiatric disease precluding interrogation; Inability to follow the procedures of the study, e. g. due to language barrier; Women who are pregnant or breast feeding; Intention to become pregnant during the course of the study and 2 months after surgery; Lack of safe contraception, defined as: Female participants of childbearing potential, not using and not willing to continue using a condom in addition to a medically reliable method of contraception for the entire study duration and 2 months after surgery, such as oral, injectable, or implantable contraceptives, or intrauterine contraceptive devices, or who are not using any other method considered sufficiently reliable by the investigator in individual cases. Female participants who are surgically sterilised / hysterectomised or post-menopausal for longer than 2 years are not considered as being of child bearing potential. male participants need to use a condom for the whole study period and 2 months after surgery; unable to consent, e. g. patients incapable of judgment needing next-of-kin consent or under tutelage; participation in another study with an investigational drug within the 30 days preceding and during the present study; previous enrolment into the current study; enrolment of the investigator, his/her family members, employees and other dependent persons.