A case is reported of swelling over the mastoid process due to subgaleal abscess possibly secondary to trivial cutaneous trauma. The diagnosis was difficult as subgaleal abscess is an extremely rare condition especially after the advent of the antibiotic era. The route of entry of the infection to the subgaleal space was unclear as there was no skin puncture. The absence of substantial trauma excluded subgaleal haematoma as a precondition. We would like to discuss the possible aetiologies and the management of this rare case in the light of the limited information available in the world literature.