Inclusion Criteria:
- Participants who had successfully completed a Phase 1, 2, or 3 tolvaptan ADPKD or renal impairment study, with a confirmed diagnosis of ADPKD from prior studies [either 156-04-251 (NCT00428948) or 156-04-250 (NCT00413777), 156-06-260, 156-09-284 (NCT01336972), 156-09-285 (NCT01210560), and 156-09-290 (NCT01451827)].
Exclusion Criteria:
- Participants unable to provide written informed consent.
- Participants (men or women) would not adhere to the reproductive precautions as outlined in the Informed Consent Form.
- Participants (women only) with a positive urine pregnancy test.
- Participants who were pregnant or breast-feeding.
- Participants unable to take oral medications.
- Participants who had allergic reactions to tolvaptan or chemically related structures such as benzazepines (benzazepril, conivaptan, fenoldopam mesylate, or mirtazapine).
- Participants with disorders in thirst recognition or an inability to access fluids.
- Participants with critical electrolyte imbalances, as determined by the investigator
- Participants with or at risk of significant hypovolemia, as determined by investigator.
- Participants with significant anemia, as determined by investigator.
- Participants with a history of substance abuse (within the last 3 years).
- Participants who were taking other experimental (that is, non-marketed) therapies or were participating in another clinical drug or device study; participating in the off-drug follow-up period of another ADPKD trial with tolvaptan was permitted.
- Participants unable to complete magnetic resonance imaging (MRI) assessments (for example, participants with ferro-magnetic prostheses, aneurysm clips, severe claustrophobia).
- Participants who had taken a vasopressin antagonist (outside of previous participation in a tolvaptan study).
- Participants unable to comply with anti-hypertensive or other important medical therapy.
- Participants with advanced diabetes.
- Participants who were taking medications or had an illness that could confound endpoint assessments (including taking approved therapies for the purpose of affecting polycystic kidney disease [PKD] cysts).