We here report two cases of Adie's tonic pupil, associated with clinical sensory polyneuropathy and Sjögren's syndrome, in one of whom it actually heralded the onset of the syndrome. Electrophysiology studies indicated absent H reflexes but normal peripheral nerve conductions, thus suggesting an involvement of the dorsal roots or spinal ganglion that would be in line with previously published reports of dorsal ganglionitis as the primary neuropathological lesion in Sjögren's syndrome. We suggest that all cases of tonic pupils should be screened for polyneuropathy and Sjögren's syndrome.