Objective To assess the features of transcranial sonography (TCS) in Parkinson disease (PD) and Alzheimer disease (AD).Methods Totally 38 PD patients (PD group),28 AD patients (AD group) and 26 controls (control group)underwent TCS.The echogenicity of the substantia nigra,widths of third ventricle and parameters of middle cerebral artery among the three groups were analyzed.Results The ratio of hyperechogenicity of substantia nigra in PD group (31/38,81.58％) were higher than those in AD group (8/28,28.57％) and control group (3/26,11.54％;x2 =18.74,30.41,both P＜0.001),and there was no significant difference in hyperechogenicity of substantia nigra between AD group and control group (x2 =2.41,P=0.120).The widths of third ventricle in AD group ([0.82±0.14]cm) were wider than those in PD group ([0.63±±0.16]cm) and control group ([0.56±0.16]cm,both P＜0.001),and there was no significant difference in widths of third ventricle between PD group and control group (P=0.098).The mean velocities in bilateral middle cerebral artery in AD group were lower than that of in PD group and in control group (all P＜0.05).The pulsatility index in right middle cerebral artery in AD group were greater than that in PD group and control group (both P＜0.05).Conclusion According to the changes of echogenicity of substantia nigra,widths of third ventricle and parameters of middle cerebral artery,TCS may provide some useful information for diagnosis of PD and AD.