In this study we examined and compared the 5' flanking regions (promoter regions) of human and murine 17beta-hydroxysteroid dehydrogenase type 7 genes (HSD17B7). In 1998, this enzyme was described to convert estrone to biologically more active estradiol. However, in 2001, it was predicted to be involved in cholesterol biosynthesis. To elucidate the mechanism governing HSD17B7 expression and its function, we analyzed the promoter regions by bioinformatic and experimental approaches. Our study provides new insights to the transcriptional regulation of HSD17B7 and further hints to its involvement in cholesterol biosynthesis.