BACKGROUND: Prolonged physical impairments are often reported post total hip replacement (THR). It is unclear which exercises should be performed to maximise rehabilitation following surgery. PURPOSE: The aim of this pilot study was to describe a method of imaging the relaxed posterior gluteus medius muscle in patients following surgery, and to measure the secondary outcome of relaxed muscle thickness of the posterior gluteus medius on the side of their THR following a rehabilitation intervention in this patient group. METHOD: This was a randomised controlled pilot study investigating the effect of functional exercise on the relaxed muscle thickness of the posterior gluteus medius as measured by real-time ultrasound. 57 patients were randomised to either a functional exercise class or usual care group. Real time ultrasound scanning of the posterior gluteus medius muscle were undertaken in both groups at baseline (week 12) and post intervention (week 18). RESULTS: There was no significant difference found in the size of the posterior gluteus medius between the intervention and control groups over the six week period of intervention. There was a statistically significant increase in the size of the posterior gluteus medius muscle at three points with a mean difference of 0.78 (95% CI 0.53-1.03), 1.05 (95% CI 0.67-1.43), 1.01 (95% CI 0.56-1.5) on the operated side in both groups over the six week period (p < 0.000). CONCLUSION: The thickness of the posterior gluteus medius on the operated side increased over a six week period from week 12 to week 18 post THR. There was no difference found in the thickness of the posterior gluteus medius in those attending a functional exercise class twice weekly and those receiving usual care.