Background: Sepsis and multiple organ failure are associated with severe complications in patients admitted at Intensive Care Unit (ICU) especially Critical Illness Polyneuropathy (CIP) and Myopathy (CIM). Those are associated with immobilization and known to increase mechanical ventilation duration, length of stay and risk of death. Early screening with motor peroneal nerve test (PENT) and sensory sural nerve test may be useful screening tools to recognize these neuromuscular complications. Aim: To record peroneal nerve test (PENT) and sensory sural nerve action potentials (SNAP) in patients suffering from septic shock and undergoing mechanical ventilation for more than 72 hours and to evaluate risk factors to develop these conditions. Design: Observational study. Method: PENT screening was performed after 72 hours of intubation and repeated until pathological response was detected. SNAP was tested on sural nerve in patients with pathological PENT to differentiate CIP from CIM. Clinical muscle strength examination was performed as patients awoke. Time to first in bed and out of bed mobilization was also recorded. Results: 20 patients were initially included. Two withdrew their consent. 18 patients underwent PENT testing between day 3 and day 7 with mechanical ventilation. Mean time elapsed between intubation and first intervention protocol was of 94.38 (+ 22.41) hours. 7 patients (38.9%) had CIP, 2 patients (11.1%) had CIM, 1 patient (5.6%) had CIP and CIM, 6 patients (33.3%) had pathological response associated with CIP or CIM, 2 patients (11.1%) had no peripheral deficit. CIP and CIM were therefore present in 55.6% to 88.9% of septic patients with mechanical ventilation. When tested, clinical muscle strength examination confirmed electrophysiological finding. 13 patients (72.2%) received out of bed mobilization with an average time of 10 (+ 7.54) days after admission. Conclusion: CIP and CIM are highly frequent in septic patients and can be recognized before being symptomatic.