We describe a patient who concomitantly developed chronic inflammatory demyelinating polyneuropathy (CIDP) and myasthenia gravis (MG) following cytomegalovirus (CMV) infection. Whereas CIDP and MG presumably have different immunopathogeneses, a number of reports presented cases with CIDP and MG, some of which were concomitant cases. Several reports described association between CIDP or MG, and CMV infection, although the association is still a matter of controversy. This is the first report of patients with concomitant CIDP and MG following CMV infection. The association may be coincidental, but the possibility that CMV infection triggered development of both CIDP and MG simultaneously cannot be excluded.