This article reports the case of a 45-year-old man with systemic myasthenia gravis who developed right upper eyelid ptosis. One month after thymectomy surgery, he developed bilateral upper eyelid retraction. Lid retraction in the absence of thyroid eye disease is uncommon in myasthenia gravis, although it can develop during periods of medical treatment and after thymectomy surgery. Exclusion of thyroid disease is essential before ascribing lid retraction to myasthenia gravis.