The use of integrative Korean medicine treatment (IKMT) for patients with knee osteoarthritis (OA) has been reported previously; however, to date, no studies have investigated the long-term prognosis of these patients following IKMT for primary knee OA. We aimed to examine the long-term effects of IKMT in patients diagnosed with primary knee OA and receiving IKMT during hospitalization. This retrospective observational study, complemented by a follow-up survey, included patients with primary knee OA who received IKMT during hospitalization across 7 Korean medicine hospitals. The primary outcome was the Numerical Rating Scale knee-pain score, whereas the secondary outcomes were the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), EuroQol-5 dimension-5 level questionnaire (EQ-5D-5L), and Patient Global Impression of Change scores. Patients were evaluated at admission, discharge, and during follow-up. Of the 180 included patients, 81 responded to the survey. Compared with the corresponding values at admission, the Numerical Rating Scale score decreased by 2.44 (2.08–2.81) points at discharge and 1.89 (1.5–2.26) points at follow-up. Additionally, compared with their scores at admission, the WOMAC score decreased by 17.20 (13.68–20.71) points at discharge and 25.74 (22.22–29.26) points at follow-up, whereas the EuroQol-5 dimension-5 level questionnaire score improved by ‐0.15 (‐0.18 to ‐0.12) points at discharge and ‐0.12 (‐0.15 to ‐0.09) points at follow-up. The patients expressed high satisfaction with pharmacopuncture (65.4%), acupuncture (54.03%), physical therapy (35.8%), and herbal medicine (34.6%). Regarding Patient Global Impression of Change, 96.30% of the patients reported improvement. IKMT was effective in improving pain, functional disability, and quality of life in patients with primary knee OA. Its effects were maintained throughout the long-term follow-up period, and physical functions continuously improved.