The government neonatal screening program has a 17-years history. Therefore, it can now provide information on the prevalence of endocrine and metabolic diseases which included in neonatal screening. Knowledge of the prevalence of metabolic diseases is very important with these results, the most effective screening methods can be determined and diseases can be identified that should be added to neonatal screening. For these purposes regular follow-up of patients with metabolic diseases and quality assuarance are also needed.