Postganglionic cholinergic dysautonomia is a relatively uncommon disease that manifests as an acute and selective dysfunction of the parasympathetic and sympathetic sudomotor nervous system. Here, we present a 27-year-old woman who suffered from subacute onset of bladder paresis. The clinical and laboratory examinations revealed a selective parasympathetic dysfunction including dilated pupils and decreased tearing without an involvement of the sympathetic sudomotor system. From clinical and laboratory evidences, it is suggested that the tonic pupil and postganglionic cholinergic dysautonomia may not be a completely different disease entity but share the same pathogenesis, which is separated only by the severity or the extent of the disease. The patient was diagnosed as 'incomplete postganglionic cholinergic dysautonomia'.