Branched-chain organic acidurias or organic acidemias are a group of disorders that result from an abnormality of specific enzymes involving the catabolism of branched-chain amino acids (BCAAs). Collectively, the most commonly encountered are maple syrup urine disease (MSUD), isovaleric aciduria (IVA), propionic aciduria (PA) and methylmalonic aciduria (MMA). They can present clinically as a severe neonatal onset form of metabolic distress, an acute, intermittent, late-onset form, or a chronic progressive form presenting as hypotonia, failure to thrive, and developmental delay. Other rare disorders involving leucine, isoleucine, and valine catabolism are 3-methylcrotonyl glycinuria, 3-methylglutaconic (3-MGC) aciduria, short/branched-chain acyl-CoA dehydrogenase deficiency, 2-methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency, isobutyryl-CoA dehydrogenase deficiency, 3-hydroxyisobutyric aciduria, and malonic aciduria. All the disorders can be diagnosed by identifying acylcarnitines and other organic acid compounds in plasma and urine by gas chromatography-mass spectrometry (GC-MS) or tandem MS and all can be detected by newborn screening using tandem MS.