S.D. Codified Laws § 27A-8-17
Thirty days after the voluntary admission of a patient and every ninety days thereafter, the facility director or center administrator shall review the patient's record and assess the need for continued admission. If continued admission is indicated, the facility director or center administrator shall consult with the patient and request from the patient an oral and written affirmation of his informed consent to continued admission. If a patient was admitted upon substituted informed consent as provided in § 27A-8-18.1, and continues to be incapable of exercising an informed consent to continued admission, a substituted informed consent to continuing admission shall be obtained as provided in that section. The notification, request, and affirmation shall become part of the patient's record. A failure to affirm substituted informed consent to continued admission constitutes notice of an intention to terminate inpatient treatment as provided in § 27A-8-10.
SDCL 27A-8-17