AIM: To investigate the pattern of diurnal variations of choroidal thickness of macular region of healthy individuals. METHODS: A prospective study of 32 healthy female subjects was conducted. Each subject underwent 1) a questionnaire on daily schedule, 2) the Pittsburgh Sleep Quality Index questionnaire (PSQI), and 3) ocular examinations including an eye dominance test, fundus photography, and sequential optical coherence tomography (OCT) imaging, on two separate days at five fixed 3h time intervals. Choroidal thickness was measured by two masked graders. RESULTS: A significant diurnal variation of choriodal thickness at fovea (P<0.001), at 500 mu m nasal (P<0.001), temporal to fovea (P=0.01) or 1500 mu m nasal to fovea (P=0.001) was observed. The median choroidal thickness peaked at 11:00 at fovea (P=0.01), at 500 mu m nasal (P=0.009) and temporal (P=0.03) to fovea. The median amplitude of foveal choroidal thickness was 20.5 mu m (13, 31) and 20.0 mu m (12.5, 28.2) for the first and second series of measurements, respectively. The greater amplitude of foveal choroidal thickness was associated with thickner initial foveal choroidal thickness [0.05 (0.03, 0.08), P=0.01], dominant eye 10.51 (4.02, 14.60), P=0.04] in the multivariate linear regression. CONCLUSION: Our data show a significant diurnal variation of the choroidal thickness at fovea, at 500 mu m nasal and temporal to fovea and 1500 mu m nasal to fovea. Thicker initial foveal choroidal thickness and being dominant eye may influence the amplitude of foveal choroidal thickness.