The discovery of biotinidase (BTD) deficiency, an inherited biotin-responsive disorder has increased the interest in biotinidase. Impaired serum BTD activity has been reported in patients suffering from chronic liver diseases, and in rats with experimentally induced acute or chronic liver injury. Molecular biology techniques such as tandem mass spectrometry have added a new dimension to our understanding of the role for biotinidase in cellular metabolism that go beyond the classical roles for biotinidase in the recycling of biotin. Recently, biotinidase has been implicated in the diagnosis of cancers. Decreased BTD is suggested as a potential serological biomarker for the detection of breast cancer .Recent reports suggests the potential applicability of biotinidase in the fine needle aspiration (FNA) diagnosis of aggressive papillary thyroid cancer. The exact role of biotinidase in cancer remains to be established. Histone biotinylation is considered to play an important role in signaling DNA damage. As biotinylation of histones depends on biotin supply it may be decreased in BTD deficient patients thereby affecting signaling of DNA damage. Elevated serum biotinidase activity has been reported in patients with glycogen storage diseases. The focus of this review is to update the metabolic importance of biotinidase and to present the applications of BTD in the diagnosis of liver diseases and recently, certain cancers.