Prader-Willi Syndrome (PWS) is characterized by hyperphagia, severe obesity, and mental retardation from early childhood and occurs 1/10,000 to 1/15,000 live births in Japan. There is high prevalence of diabetes mellitus because of hyperphagia. The patient may sometimes face the necessity of renal replacement therapy (RRT) because of end-stage kidney disease (ESKD) caused by diabetes-associated kidney disease (DKD). Since mental retardation and extreme obesity usually prevent to introduce peritoneal dialysis (PD), hemodialysis (HD) has been the first choice of RRT. In this report, we experienced one case of patient with PWS suffering from ESKD due to DKD who started PD as an initial RRT and succeeded to continue for total of 40 months. The patient was 37-year-old man at the time of initiation of dialysis. PD was chosen for RRT because we suspected that he might have more technical difficulties for continuing HD. After several episodes of peritonitis, he successfully continues PD without peritonitis for next 27 months until the present time with good support by his family member. To our best knowledge, this is the first reported case of ESKD associated with PWS who was successfully treated with PD for long period.