['Ultrasonography has been used as a non-invasive approach to measure skin thickness. To date there have been no studies on diurnal variations in skin thickness.', 'To evaluate diurnal variations in skin thickness and to compare these with corresponding echogenicity and skin elasticity.', 'Measurements by ultrasonography B-mode and by Cutometer SEM 575 were carried out in the morning and in the afternoon on 20 men and 20 women (mean age 30 years) on three areas of the face (forehead, corner of the eye and cheek), the forearm and the upper arm, and the flank, thigh and calf.', 'From the morning to the afternoon, the skin thickness in both sexes significantly decreased on three areas of the face, the forearm and the upper arm, but significantly increased on the thigh and calf. In parallel, the echogenicity significantly increased from the morning to the afternoon on the three areas of the face, the forearm and the upper arm, but decreased significantly on the thigh and calf. Measurements of mechanical properties at four sites demonstrated that from the morning to the afternoon, the major parameters of skin elasticity Ue* and Uf* increased significantly in both sexes on two areas of the face and slightly on the forearm, but decreased significantly on the calf.'] Is dermal fluid translocation an important determinant of the diurnal variation in human skin thickness?