This case report presents a 28-year-old man with foot drop 48 hours after a grade I inversion ankle sprain. Clinical examination and electrodiagnostic studies showed common peroneal nerve palsy. The patient was managed with conservative treatment and rehabilitation and recovered completely 4 months after the injury. Physicians should be aware of the possibility of delayed peroneal nerve injury after grade I ankle sprain. Function of the peroneal nerve should be evaluated in all patients with inversion ankle sprain as part of initial and follow-up evaluations. Early electrodiagnostic studies are helpful to localize and provide indications of the severity of the injury.