Introduction: As a result of mastectomy, physical fitness deteriorates, balance disorders and lymphoedema of the upper limb occur, which undoubtedly affect the level of stability among women following this surgery. Complex physical therapy in this group of patients is one of the key aspects influencing the level of physical activity among women subjected to surgery.Research objective: The aim of the study was to assess the impact of complex physiotherapy on physical fitness and balance in women following unilateral mastectomy with lymphoedema of the upper limb. Additionally, it was analysed whether wearing an external breast prosthesis affects the postural stability of women after mastectomy.Materials and methods: The study group comprised 30 women post unilateral mastectomy, 51 to 78 years of age, with upper limb lymphoedema. Before starting and after completing the physical therapy programme, the examined women were asked to perform the Timed Up and Go (TUG) Test and the Static Postural Stability Test on the Biodex Balance System platform. The tests were performed at the Posturology Laboratory of the Collegium Medicum, Jan Kochanowski University in Kielce.Results: In the analysis of the results of the Timed Up and Go Test in women following unilateral mastectomy, better results were noted after completion of physiotherapy in all 3 trials (p=0.001, p=0.021, p=0.004), as well as in the Postural Stability Test for all test parameters. The Mann-Whitney U test allowed to indicate a statistically significant difference in the values of the general stability index (p=0.005) and the A/P stability index (p=0.004). Greater body sway dominated in the sagittal plane than in the frontal one (A/P > M/L). On the other hand, in posturographic examination, external prostheses did not affect the postural stability of post-mastectomy women.Conclusions: 1. Systematic motor exercises in women following unilateral mastectomy are an important element of maintaining required physical activity, and they also prevent posture-related disorders; 2. The use of an external breast prosthesis in women after unilateral mastectomy does not significantly cause a change to body posture.