Being able to decipher paleo sea surface temperatures for warm oceanic waters is of the utmost importance to further evaluate the role of the tropics in global climate change. The UK'37 index is one of such paleothermometers, although the warm range of temperatures often poses serious analytical challenges. This paper discusses and reviews several important aspects of the UK'37 index calibration for waters warmer than 26¿--27¿C. Amongst them, insights into the possible existence of a limit above which the UK'37 index is not able to accurately record temperature variations are presented. Some warnings are also given on the misleading practice and expected consequences of reporting UK'37 index values of unity in the cases when abundances of the minor triunsaturated alkenone below detection limit are encountered. Future directions toward an improved knowledge of the behaviour of the UK'37 calibration for warm waters are suggested.