Propionic acidemia (PA) is a disorder of organic acid metabolism caused by deficient activity of mitochondrial propionyl-CoA carboxylase. Onset often occurs in the neonatal period and is associated with developmental delay and early death. The common clinical presentation includes severe ketoacidosis, vomiting, poor feeding, lethargy, hypotonia and coma. Hyperammonemia, seizures and hepatomegaly may also be present. A small number of patients have only exhibited neurologic signs. Late-onset patients usually have a milder course.