The proxy record is derived from stalagmite YOK-I from the Yok Balum Cave, Belize. Stalagmite YOK-I was collected in June 2006, ca. 160 m from the western cave entrance. Carbonate was actively precipitating on the tip of this 606.9-mm-long stalagmite when it was collected. The stable isotope climate record covers only the upper 415 mm, while the lower stalagmite section is less suitable for stable isotope studies and was not included in this investigation. Over 4,200 δ18O and δ13C measurements were performed on the upper 415 mm of YOK-I and dated between 40 BC and 2006 AD. The samples were continuously milled at 0.1 mm increments and, depending on growth rate changes in YOK-I, the temporal resolution of the isotopic data fluctuates from 0.01 and 3.68 yrs/0.1 mm, with an average resolution of 0.49 yrs/0.1 mm. Earlier versions of the dataset have been published at the NOAA palaeoclimate data server using a slightly different chronology (Kennett et al., Science 2012, DOI:10.1126/science.1226299). In the study of Ridley et al. (Nat Geo 2015, DOI:10.1038/ngeo2353), we have tuned the chronology of YOK-I with the more precise one of the stalagmite YOK-G. These new data is provided as version 2 in the files YOK-I_d18O_v2.csv (for δ18O) and YOK-I_d13C_v2.csv (for δ13C), consisting of 4047 isotope measurements. Kernel filtering was applied to resample the time series to equidistant annual resolution (Smirnov et al, Sci Rep XXX, DOI: XXX), covering the time span from 15 BC to 2005 AD, resulting in 2021 data values. These filtered versions of the data are provided as files YOK-I_d18O_kernelfiltered.csv and YOK-I_d13C_kernelfiltered.csv. In all files, the first column consists of the age (in yr AD) and the second column (separated from the first column by a semicolon) is the corresponding isotope value (in permil VPDB). The data is presented as four .csv files in a .zip folder.