Infectious mononucleosis is usually produced as primoinfection by Epstein-Barr virus, but the second most common cause is cytomegalovirus. Clinical presentation of infectious mononucleosis is a pharyngitis and tonsillitis, associated to neck nodes, fever and general malaise, as well as haematological features such as an absolute lymphomonocytosis. Occasionally it is the neck node that is more severe, even without initial lymphomonocytosis. We report a deep neck abscess within a neck node as subacute presentation of infectious mononucleosis by cytomegalovirus. We review the clinical presentation of infectious mononucleosis, specially due to cytomegalovirus, as well as the importance that this disease could have while dealing with diagnosis and management of neck masses.