Muscular involvement is rare, representing less than 1% of hydrated cyst localisation's. Clinical symptoms are insidious and non-specific causing a frequent delay in diagnosis. We report the observation of a 50 year-old woman consulting for inguinal tumefaction with radiological exploration suggestive of hydrated cyst of adductors muscles. Magnetic resonance imaging is helpful in diagnosis, since it reveals a very suggestive aspect. Treatment is based on surgery, which cures patients but incurs a low risk of local relapse.