We evaluated the occurrence of cytomegalovirus (CMV) infection and the background characteristics in twenty-three hospitalized patients with inflammatory connective tissue diseases including systemic lupus erythematosus, polymyositis/dermatomyositis, rheumatoid vasculitis, microscopic polyangitis, and Takayasu's arteritis. Cytomegalovirus antigenemia was demonstrated in 10 of 23 evaluable patients. Five of ten patients with CMV antigenemia developed symptomatic CMV disease (all cases of fever, two cases of liver involvement, two cases of interstitial pneumonia, and one case of unknown organ involvement), whereas the remaining five patients were asymptomatic. Most of CMV antigenemia-positive patients had been administered intravenous steroid pulse, or in combination with immunosuppressive agents intravenously or orally because of refractory disease activity. Particularly, in patients who received intravenous methylprednisolone pulse in combination with additional intravenous cyclophosphamide pulse, the incidence of CMV antigenemia was markedly higher (four out of four). Four of ten CMV antigenemia-positive patients simultaneously showed detection of Pneumocystis jiroveci in induced sputum by PCR, increase in level of serum beta-D-glucan and the finding of geographical ground-glass opacities on chest computed tomography. These findings suggested that patients with connective tissue diseases under intensive immunosuppressive therapies (intravenous steroid pulse in combination with additional intravenous cyclophosphamide pulse in particular) are highly susceptible to CMV infection and disease, and that patients complicated by CMV antigenemia are susceptible to combined opportunistic infection such as Pneumocystis pneumonia.