Among the different species of Crocus, only C. sativus has been extensively studied for the composition and the biological properties of its styles, since these constitute the well-known spice saffron, which is widely used in the Mediterranean, Indian and Chinese diet. With high performance liquid chromatography (HPLC) and UV/vis spectroscopy, the presence of hydrophilic carotenoids in the styles of three other Crocus taxa, endemic in Greece, C. boryi ssp. tournefortii, C. boryi ssp. boryi and C. niveus, is reported for the first time. Incubation of MCF-7 and MDA-MB-231 breast cancer cells for 48 h with different concentrations of all four Crocus style extracts showed a dose-dependent inhibitory effect on cell proliferation measured by the MTT assay. The antiproliferative effect was not related to the presence of estrogen receptors. Studies on the effect of trans-crocin-4 (the main carotenoid constituent of C. sativus styles, digentibiosylester of crocetin), crocetin and safranal showed that the antiproliferative effect is attributed to the constituent crocins irrespective of the degree of glycosylation. These results show that the styles of the various Crocus taxa merit further investigation of their composition and mechanisms of action of their carotenoid constituents in order to establish if they could be used as chemopreventive or anticancer agents.