In this paper, we evaluate the effects of time separation between acquisitions in iris recognition. We use for our experiments a publicly available iris recognition system and the BiosecurlD database, containing 8128 iris images of 254 individuals acquired in four acquisition sessions, separated by one to four weeks between consecutive sessions. Reported results show that time separation between iris samples under comparison has severe impact on the recognition rates. An important degradation on the False Rejection Rate is observed, meaning that the intra-class variability is increased. All images in our database have been acquired under similar controlled conditions and with the same sensor. © 2008 IEEE.