ABSTRACT: Introduction: At least 25% of knee dislocations are associated with common fibular nerve injury. Diagnosis is usually based on clinical and neurophysiological findings. We assessed the role of nerve ultrasound in common fibular nerve injury. Methods: Eight consecutive patients (6 men and 2 women, mean age 34 years) with knee luxation referred to our laboratory underwent clinical, neurophysiological, and ultrasound examination. Results: In all patients we observed a similar pattern: severe weakness (plegia or severe paresis); neurophysiological involvement of both fibular nerve branches; and ultrasound evidence of increased fibular nerve area with hypoechogenicity. On follow-up evaluation, 6 patients remained stable, and 2 patients improved. The greater the ultrasound fibular nerve enlargement, the worse the recovery. Conclusions: Nerve ultrasound was confirmed to be a useful diagnostic/prognostic tool in traumatic nerve lesions. A prompt ultrasound examination of the fibular nerve should be considered after any case of knee dislocation