Organic acid analysis detects accumulation of organic acids in urine and other body fluids and is a crucial first-tier laboratory test for a broad spectrum of inborn errors of metabolism. It is also frequently ordered as follow-up for a positive newborn screen result, as recommended by American College of Medical Genetics and Genomics newborn screening ACTion sheets and algorithms. The typical assay is performed by gas chromatography-mass spectrometry. These technical standards were developed to provide guidance for laboratory practices in organic acid analysis, interpretation, and reporting. In addition, new diagnostic biomarkers for recently discovered organic acidurias have been added.