Background: Phenylketonuria (PKU) is a well-known rare disease which is included in the neonatal screening of many countries. Therefore there are few published data on the admissions and cost in Spain.Objective: To assess the number of admissions and economic burden of PKU in Spain.Methods: PKU patients were identified from a Spanish database containing data from public and private healthcare centres from 1997 to 2015. The parameters obtained were: characteristics of the patients, type of admissions, readmissions, discharge, length of stay, medical service, annual number of visits, annual number of patients, visit associated costs and patient associated costs.Results: 594 PKU patients were identified: 48.32% were males with a mean (SD) age of 4.50 (10.23) years. The hospital admissions were divided into emergency visits (55.94%) and scheduled visits (43.92%). Most of the discharges were at home (98.86%). The mean (SD) duration of stay was 4.04(4.98) days.