Knee and hip joint replacements for the elderly are increasingly placing a burden on healthcare. Our aim was to verify the efficiency of the prehabilitation program among patients with knee arthroplasty (TKA) and hip arthroplasty (THA), taking into account the length and cost of postoperative rehabilitation and the restoration of function. We introduced a two-week preoperative physiotherapy program for patients awaiting knee and hip replacement surgery. We measured the duration and costs of the hospital stays, the active and passive range of motion of the hip and knee joints, and the quality of life. In the study, 99 patients participated (31 male, 68 female), with a mean age of 69.44 ± 9.69 years. We showed that, as a result of the prehabilitation program, the length of postoperative hospital stay decreased (THA: median 31.5 (IQR 26.5–32.5) vs. median 28 (IQR 21–28.5), TKA: median 36.5 (IQR 28–42) vs. median 29 (IQR 26–32.5)), and the patients’ quality of life showed a significant improvement (TKA: median 30.5 (IQR 30–35) vs. median 35 (IQR 33–35), THA: median 25 (IQR 25–30) vs. median 33 (IQR 31.5–35)). The flexion movements were significantly improved through prehabilitation in both groups. Based on our positive results, we recommend the introduction of prehabilitation into TKA- and THA-related care.