The aim of the study was to evaluate the subjective functional outcome of total hip arthroplasty (THA) in patients who underwent hydrotherapy (HT) 6 months after discharge. A prospective randomized study was performed on 70 elderly inpatients with recent THA, who completed a rehabilitation program. After randomization, 33 of them were treated in conventional gyms (no-hydrotherapy group=NHTG) and 31 received HT (hydrotherapy group=HTG). Interviews with the Western-Ontario MacMasters Universities Osteoarthritis Index (WOMAC) were performed at admission, at discharge and 6 months later. Kruskal-Wallis, Mann-Whitney and Wilcoxon tests were applied for statistical analysis. Both groups improved. Pain, stiffness and function were all positively affected. Statistical analysis indicated that WOMAC sub-scales were significantly lower for all patients treated with HT. The benefits at discharge still remained after 6 months. We conclude that HT is recommended after THA in a geriatric population.