Prader-Willi syndrome (PWS) is a complex multisystem genetic disorder due the lack of expression of paternally inherited imprinted genes on chromosome 15ql1-13. Clinical presentation includes hypotonia, hyperphagia, obesity, hypogonadism, learning difficulty. Objective: To study clinical and laboratory of patient diagnosed and treated in National Hospital of Pediatrics, Hanoi (NHP). Subjects: 28 patients diagnosed of PWS by FISH in NHP from December 2007 to April 2012 were recruited in the study. Methods: Descriptive study. Results: Male/female ratio was 6/1. Patients diagnosed before 5 years occupied 53.5 percent. 85.7 percent of patients were found to have hypotonia at age of 4.9 + or - 2.0 months. 86.4 percent of patients had hyperphagia at age of 20.7 + or - 11.1 months. In patients aged of 2 years, weight SDS was +8.7 + or - 4.7 SD compared to gender and age. The figure of BMI was +10.3 + or - 6.3 SD. 4/7 of patients aged or = 6 years had micropenis. 100 percent of patients had mental retardation. 91.7 percent of patients had cryptorchidism. 4/24 of patients (14.3 percent) had type 2 diabetes mellitus. Conclusion: Based on clinical presentation, more PWS patients could be diagnosed and treated early.