The Forgotten Joint Score-12 (FJS-12) is a valid patient-reported outcome measures (PROMs) used to assess prosthesis awareness during daily activities after total hip arthroplasty (THA). The minimum clinically important difference (MCID) can be defined as the smallest change or difference that is evaluated as beneficial and could change the patient's clinical management. The patient acceptable symptom state (PASS) is considered the minimum PROMs cut-off value that corresponds to a patient's satisfactory state of health. Despite the validity and reliability of the FJS-12 having been already demonstrated, the MCID and the PASS of this score have not previously been defined. Patients undergoing THA from January 2019 to October 2019 were assessed pre-operatively and six months post-surgery using the FJS-12, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Oxford Hip Score (OHS). Pre-operative and follow-up questionnaires were completed by 50 patients. Both distribution-based approaches and anchor approaches were used to estimate MCID. The aim of this paper was to assess the MCID and PASS values of FJS-12 after total hip replacement. The FJS-12 MCID from baseline to 6 months post-operative follow-up was 17.5. The PASS calculated ranged from 69.8 to 91.7.