Methylmalonic acidemia (MMA) is an autosomal recessive disorder of methylmalonate and cobalamin (cbl; vitamin B12) metabolism. It results commonly from a defect in the gene encoding methylmalonyl CoA mutase apoenzyme MCM (mut MMA or vitamin B12-unresponsive MMA). This work highlights four aspects of methylmalonic aciduria diagnosis: First, it presents an overview of the diagnostic evaluation of patients with organic acidurias and several other IEMs by liquid chromatography- tandem mass spectrometry (LC-MS/MS), gas chromatography- mass spectrometry (GC-MS) and isocratic “high-performance liquid-chromatography” (HPLC).Second, it reports HPLC method for screening of disease associated metabolites and compares the specificity and sensitivity of HPLC and GC/MS for organic aciduria screening. Third, it reports the clinical and biochemical laboratory investigations to MMA, and finally was to highlight the molecular investigations by reporting the results of mutation study of exon II of MUT gene for all patients with methylmalonic aciduria. Findings are likely to be of great interest to the scientists, researchers, trainees and clinicians and could be applied in the clinic right away.