BACKGROUND: Acquired unilateral ptosis usually results from either levator palpebrae disinsertion, eyelid disorder, myasthenia gravis, mitochondrial myopathy, Horner's syndrome, or third nerve palsy. In rare cases, an orbital process is responsible for ptosis or pseudoptosis. HISTORY AND SIGNS: A healthy 31-year-old patient complained for 6 months of right eyelid ptosis. On examination, there was 1 mm right upper eyelid ptosis and 1 mm of right enophthalmos. Upon downgaze, an apparent right eyelid retraction was present. Magnetic resonance imaging showed filling and retraction of the right maxillary sinus with inferior displacement of the right orbital floor. THERAPY AND OUTCOME: Surgical management was performed with a favourable outcome. CONCLUSIONS: Silent sinus syndrome is an asymptomatic chronic maxillary sinus atelectasis, resulting in ipsilateral enophthalmos, hypoglobus, and occasionally eyelid pseudoptosis. Silent sinus syndrome should be incorporated in the differential diagnosis of acquired unilateral ptosis.