This document summarizes cases of inborn errors of metabolism (IEM) diagnosed in the Jeddah region from 2010-2013. It presents two relatively rare case studies in more detail: a 2-year-old with Aminoacylase 1 deficiency who is developing normally, and a 5-year-old with 3-Methylcrotonyl-CoA carboxylase (3MCC) deficiency who is managing well with a leucine-free diet and carnitine. Overall, the document provides statistics on various IEM cases diagnosed, discusses the classification and presentation of small-molecule disorders and lysosomal storage disorders, and reviews the diagnosis and management of Aminoacylase 1 deficiency and