One approach to studying the role of sphingolipids in biological systems is to study inborn errors of metabolism. These are diseases in which the mutated gene encodes most typically an enzyme that is involved either in sphingolipid biosynthesis or catabolism. I will discuss the insights that have been gained from studying these rare disorders and how these diseases are shedding light on pathogenic mechanisms in both rare and common diseases. The information gained has resulted in multiple therapies that are at various stages of the development/approval pathway, that all target different steps in the very complex pathogenic cascades characteristic of these diseases.