Many inherited conditions result from disorders of intermediary metabolism. Many more are discovered annually using advanced gene sequencing and other tools. These diseases cause symptoms because of the accumulation of precursors, absence of the final product, excessive toxic intermediaries, or a combination of all three mechanisms. Many are fatal in childhood, but some are compatible with adult life and pregnancy. A better understanding of the enzymatic deficiencies and new technologies have made recombinant enzyme replacement therapy possible. Along with early diet manipulation, current management allows many patients to live relatively normal lives. Because fertility may not be affected, some of these conditions will be encountered by the anesthesiologist. This chapter describes diseases caused by certain enzyme deficiencies and the by-products that cause symptoms. Some are exacerbated by pregnancy and the stress of labor and delivery. The anesthesiologist plays an essential role in reducing physiologic stress and avoiding triggering agents and routines that cause severe metabolic derangements or cardiopulmonary decompensation. The final portion of the chapter describes the most recent advances in the prevention and treatment of malignant hyperthermia in pregnancy, discussing the impact on mother and baby.