Objective: To investigate the impact of aquatic exercise on pressure pain threshold in breast cancer survivors with hormone therapy-associated arthralgia. Design: Single-blind, controlled trial. Setting: Two major metropolitan hospitals and a Sport and Spa Club in Granada, Spain. Subjects: Forty women aged 29-71 years with stage I-III breast cancer who reported arthralgia. Intervention: Patients were allocated alternately to either aquatic exercise in a chest-high pool or usual care while on the waiting list; control patients received treatment later. The two-month hydrotherapy intervention consisted of 24 sessions 3 days per week. Each session included 5 minutes of warm-up, 15-20 minutes of aerobic exercise, 15 minutes of mobility exercise and 20 minutes of recovery techniques. Main measures: Pressure pain threshold at neck, shoulder, hand and leg were evaluated as primary outcomes. Cancer-related fatigue, as measured by the Piper Fatigue Scale, body mass index and waist circumference were secondary outcomes. A 2 x 2 repeated-measure ANCOVA was used in this study. Results: No adverse events or development of worsening of pain was observed. Almost all the participants in the intervention group (89%) adhered to the hydrotherapy programme. Participants experienced a decrease in pressure pain threshold measured in neck, hand, shoulder and leg, as measured by algometry pressure, and waist circumference; all P < 0.05. Cancer-related fatigue (P = 0.06) and body mass index (P = 0.42) did not show significant improvement. Conclusions: These data suggest that hydrotherapy in a chest-high pool may reduce the pain threshold and waist circumference in breast cancer survivors with hormone therapy-associated arthralgia.