Perioperative complications following bariatric surgery (BS) have been poorly analysed and their management is not clearly assessed. The associated frequency of ICU admission is difficult to estimate. Among surgical complications, digestive perforations are the most frequent. The most common postoperative complications of sleeve gastrectomy are fistulas, but bleeding on the stapling line is also commonly reported. Complication rates are higher after Roux-en-Y gastric bypass, mainly due to anastomotic leaks. Medical complications are mainly thromboembolic or respiratory complications. All these surgical and medical complications are not easily detected; clinical signs can be atypical or insidious, often resulting in delayed management. Respiratory signs can be predominant and lead erroneously to pulmonary or thromboembolic diseases. Diagnostic criteria are based on minor clinical signs, tachycardia being probably the most frequent one. Lately, complications are revealed by haemodynamic instability, respiratory failure or renal dysfunction and radiographic findings. Management decision according to these abnormal signs is based on a combined multidisciplanary approach including surgical and/or endoscopic procedures and medical care, depending on the nature and severity of the surgical complication. Medical management is based on supportive ICU care of organ dysfunctions, curative anticoagulation if required, nutritional support, and appropriate anti-infective therapy. Pharmacological data are limited in morbidly obese patients and the appropriate doses are debated, especially for anti-infective agents. Complicated BS cases have a poor outcome, probably largely related to delayed diagnosis and reoperation.