OBJECTIVE Corneal topography and thickness has clinical importance in contact lens fitting and refractive surgery, however repeated measurement of corneal thickness and curvature is complicated by the natural phenomenon of diurnal variation. Our aim was determine diurnal variations of central and paracentral corneal thickness and curvature over a period of ten hours. METHODS Corneal thickness and curvature of 10 right eyes of 10 young healthy men were determined by Orbscan Topography System and EyeSys videokeratoscope respectively. Both parameters were determined for central and paracentral regions 1 mm and 2 mm from the centre of the cornea at 2-hour internals for ten hours. RESULTS The cornea was thickest and flattest on awakening. There was a difference in corneal thickness (ANOVA, Schfféc method p< 0.05) and curvature (ANOVA, Tamhane method p< 0.05) over time for all the corneal locations studied, with greater changes observed in the peripheral corneal data. The minimum value was 10 and 8 hours after eye opening for central and paracentral zones, respectively. Change in central and paracentral corneal thickness was strongly correlated with corneal curvature, except for the 2 mm nasal and superior semi-meridians. CONCLUSIONS These data indicate a shift in corneal thickness and curvature that can be of clinical relevance as individual changes vary greatly.