Inborn Errors of Metabolism (IEM) are genetic disorders with detectable biochemical anomalies which impair normal metabolism. These include conditions with defects in the metabolism of amino acids, carbohydrates, lipids, mucopolysaccharides, etc. These disorders can become apparent immediately after birth or in a few days or weeks after birth. However, in India due to economic constraints, lack of awareness and education amongst parents in addition to scarcity of reliable investigations, many IEMs remain undiagnosed and untreated. One such rare IEM we recently came across in our centre, which was a welcome challenge to diagnose, was biotinidase deficiency. Biotinidase deficiency is a rare autosomal recessive metabolic disorder with an estimated incidence of 1:61067 population, though severe or profound disease is even more rare with an incidence of 1: 137401 population. [1] Clinically patients of biotinidase deficiency can present with a variety of neurological and dermatological signs, such as seizures, hypotonia, feeding problems, developmental delay, hearing loss, optic atrophy ataxia, alopecia, and skin rash. The objective of this case report is to analyse the clinical and laboratory profile, diagnostic challenges and outcome of a child presenting with a rare inborn error of metabolism presenting for the first time to the Paediatric intensive care unit (PICU) in a tertiary care teaching hospital, Dr. D Y Patil Medical College and Hospital, Pune.