Data from a retrospective cohort that included individuals aged 50–69 years who participated in colorectal cancer (CRC) screening in Barcelona from 2010 to 2015, and were followed until 2017 to identify interval CRCs. The positivity rate, and detection rates for advanced polyps and CRC were compared according to ambient temperature, humidity, and quarters of the year. A positive FIT was defined as the detection of ≥20 μg Hb/g in feces. The monthly ambient temperature and humidity were recorded on the day that the FIT was performed. In total, 92.273 FIT results from 53.860 participants were analyzed.