INTRODUCTION: Little is known about the day-to-day variability of different skin microcirculation parameters, and how this variability is influenced by age and sex. The aim was to examine the day-to-day variability of microcirculatory parameters in relation to age and sex. METHODS: The cutaneous microcirculation was measured using a fiber optic probe integrating laser Doppler flowmetry (LDF) and diffuse reflectance spectroscopy (DRS) to measure oxygen saturation, red blood cell (RBC) tissue fraction, speed-resolved and conventional perfusion. Measurements at two separate days were compared during baseline, a 5-min occlusion and during the following post-occlusive reactive hyperemia (PORH) period on the volar forearm and dorsal foot in totally 48 men and women aged 20-30 and 50-60 years, respectively. Variability was expressed as the coefficient of variation CV and repeatability as the intraclass correlation coefficient ICC. RESULTS: Peak oxygen saturation during PORH had the lowest day-to-day variability for the forearm (CV = 2.1 %) and the foot (CV = 3.8 %) as well as an excellent repeatability (ICC = 0.80 and ICC = 0.82, respectively). Older women had a higher day-to-day variability in baseline conventional perfusion compared to younger women on the forearm (p = 0.007). On the foot, older women had a lower day-to-day variability than younger women for baseline oxygen saturation (p = 0.006) and peak RBC tissue concentration (p = 0.008). Older men had a lower day-to-day variability than younger men for baseline oxygen saturation (p = 0.012) but a higher variability for baseline and peak RBC tissue concentration (p = 0.008 and p = 0.002) on the foot. CONCLUSION: Peak oxygen saturation had the lowest day-to-day variability of the measured parameters. A lower value of peak oxygen saturation has previously been associated with increasing systematic coronary risk implying that this is a suitable parameter for measuring microcirculatory dysfunction. Sex and age only affected the day-to-day variability of very few parameters.