This is Part II of my book (Inborn Errors of Metabolism), after Part I published previous year.The clinical manifestations of inborn errors of metabolism vary widely with both mild and severe forms of virtually every disorder. Many patients do not match the classic phenotype because mutations are not identical in different patients, even though they are in the same gene. Inborn errors can manifest at any time, can affect any organ and can mimic many common pediatric problems. Lastly, I hope this book will be beneficial for under and postgraduate colleagues. My Best regard, Elsayed Ibrahim Salama MD, PhD, MSc, MBBS.Part II - 2021