The purpose of this is study is to evaluate the long-term safety of DCCR (diazoxide choline) extended-release tablets) in patients with Prader-Willi syndrome.

Inclusion Criteria:

1. Provide voluntary, written informed consent (parent(s) / legal guardian(s) of patient); provide voluntary, written assent (subjects, as appropriate)

2. Participant must:

   1. Have participated in and completed the Study C602 Randomized Withdrawal (RW) Period;
   2. Have participated in but discontinued from the Study C602 RW Period and at least 16 weeks have elapsed since the date of their randomization into the C602 RW Period; or
   3. Have participated in Study C602 OLE period, did not consent to participate in the RW Period, and at least 16 weeks have elapsed since the date of their C602 Open-Label Extension End of Treatment Visit.

Exclusion Criteria:

1. Positive urine pregnancy test (in females of child-bearing potential)
2. Females who are pregnant or breastfeeding, and/or plan to become pregnant or to breast-feed during or within 30 days after study participation.
3. Participation in a clinical study of an investigational drug (including approved drugs for unapproved uses), investigational device, or therapeutic intervention subsequent to the C602 Open-Label Extension End of Treatment Visit.