Background: Inborn errors of metabolism (IEM) are rare genetic (inherited) disorders in which the body cannot properly turn food into energy. The disorders are usually caused by defects in specific proteins (enzymes) that help break down (metabolize) parts of food. Objectives: Determine the prevalence of inborn error of metabolism among new borne delivered in Makkah maternity hospital during the study period and assess the nutritional status of children with IEM attending the pediatric outpatient clinic of the same hospital. Subjects and methods: A Cross-sectional study was carried out including40 patients with IEM. According to Saudi Newborn Screening program, blood spots were obtained from infants at 24 - 72 hrs after birth, by heel prick technique using a standard Guthrie card and sample was dried at room temperature and analyzed by using Tandem Mass Spectrometry (MS/MS) at King Faisal Specialized Center in Riyadh. Data about socioeconomic, medical history, and dietary history were collecting using an interview questionnaire. Anthropometric measurements were taken, and laboratory investigation was done differ according to the category of IEM. Statistical analysis was performed by using the Statistical Package for Social Science (SPSS V 20). Results: The results showed that 21 patients with disorders of amino acid metabolism, 14 patients with disorders of organic acid metabolism. Disorders of carbohydrate metabolism represented by 1 case of galactosemia, and disorders of urea cycle metabolism represented by 4cases. The prevalence of global malnutrition among the whole IEM cases between 6-59 months was 28.1% and higher in girls than boys. No cases of kwashiorkor or marasmic kwashiorkor were found among the studied children, while 7 cases of marasmus were found representing 21.9%. In addition, results shows that anemia was apparent among IEM cases aged 2 months till the age of 2 years (p>0.05). Recommendations: Nutrition community program and nutrition care intervention for patients with IEM to support adequate nutrient intake is required.