Critical illness polyneuropathy (CIP) and critical illness myopathy (CIM) are frequent complications in critically ill patients and both are associated with sepsis, systemic inflammatory response syndrome (SIRS) and multiorgan failure. Major signs are muscle weakness and problems of weaning from the ventilator. Both CIP and CIM lead to elongated times of ventilation, elongated hospital stay, elongated times of rehabilitation and increased mortality. Electrophysiological measurements help to detect CIP and CIM early in the course of the disease. State of the art sepsis therapy is the major target to prevent the development of CIP and CIM. Although no specific therapy of CIP and CIM has been established in the past, the diagnosis generally improves the therapeutic management (weaning from the ventilator, early physiotherapy, etc.). This review provides an overview of clinical and diagnostic features of CIP and CIM and summarizes current pathophysiological and therapeutic concepts.