Introduction Hydrocoeles of the Canal of Nuck are a rarely reported occurrence, particularly in the adult female population. The condition results from incomplete obliteration of the processus vaginalis and tends to present with inguinal swelling. To the authors knowledge, this case represents the only reported incidence of an encysted hydrocoele of the Canal of Nuck following groin dissection and exposure. Report A 40-year-old female presented with a large mass in her right inguinal region as well as right foot and lateral leg paraesthesia ten years after a right groin vein harvest. Physical examination revealed a mildly tender, large palpable right inguinal mass adjacent to a previous surgical scar. Magnetic resonance imaging (MRI) and ultrasound revealed a 39 x 30 x 92mm septated cystic lesion in the right groin closely related to the round ligament of the uterus, favoured to represent a hydrocoele of the Canal of Nuck. Subsequent open surgical exploration, removal of a large encysted hydrocoele, and repair of the Canal of Nuck was performed. Discussion Hydrocoeles of the Canal of Nuck are extremely rare, as such, often pose a diagnostic dilemma. This case highlights that it should be considered as a differential diagnosis when assessing inguinal masses following surgery. Once recognised as a potential cause of inguinal swelling, ultrasound and MRI can accurately identify and describe this condition and assist operative planning. Complete excision and repair of the defect of the Canal of Nuck is recommended to reduce risk of recurrence.