Today's mobile phones and tablet PCs offer a considerably wider range of functionalities than before. Mobile applications (apps) are increasingly used in managing various daily health tasks. According to a recent report by the IMS Institute for Healthcare Informatics, more than 165,000 health-related apps are offered on all the stores of different platforms 1,2) . In fact, health apps, which have a share of about 3 percent of all active apps in Apple app stores 3) , have become the third-fastest growing category after games and utilities 2) . According to reports, one third of health apps were designed for more specific areas, such as professionals or people affected by a specific disease 1,2) . However, more than 50% of the available apps received less than 500 downloads, and the IMS Institute for Healthcare Informatics attribute this situation to the poor quality of many of them, the lack of guidance on the usefulness of apps, and a low level of support from health professionals 1,2) . Prader-Willi syndrome (PWS) is characterized by neonatal hypotonia, poor sucking in infancy, early-onset hyperphagia, and the development of morbid obesity in children, and GH therapy is essential for improving muscle strength and physical function, normalizing height, increasing lean body mass and mobility, and decreasing fat mass 4) . Therefore, a method for establishing appropriate and steady PWS-specified GH treatment should be provided by a PWS specialist.Pf Jin and the Association for Research on MPS and Rare Diseases (AMARD) have helped PWS families through medical information and family support since 2015. AMARD developed the first application for Korean patients with PWS, which was released to a limited number of patients under the age of 3 and only provided to Android users. The application is a valuable suppleReview Article Today's mobile phones and tablet PCs offer a considerably wider range of functionalities than before. Mobile applications (apps) are increasingly used for managing various daily health tasks. Currently, more than 165,000 health-related apps are offered on all the stores of different platforms. Pf Jin and the Association for Research on MPS and Rare Diseases (AMARD) have helped Prader-Willi syndrome (PWS) families through medical information and family support since 2015. AMARD developed the first mobile application for Korean patients with PWS, which was released to a limited number of patients under the age of 3 and only provided to Android users. The first version of the PWS application focused on growth hormone therapy and the assessment of growth and development by parents in infant and early-childhood PWS patients. The 2016 version of the PWS application has been improved in many different ways. We have expanded the subjects of the application to late childhood and adolescent groups, changed the user interface accordingly, and made the application available for iOS users. We will show the specialized growth curves of older children with PWS. Therefore, patients with PWS over the age of 3 an...