Although adding rituximab to standard cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) chemotherapy is an efficacious and well-tolerated regimen in elderly patients with diffuse large B cell lymphoma (DLBCL), it may increase susceptibility to opportunistic infections, and such cases have been reported. Our study was to identify the risk factors for fungal infection in a retrospective case-control matched study of 34 elderly DLBCL patients treated with rituximab plus CHOP (R-CHOP) and 35 control patients treated with the standard CHOP regimen at the Taipei Veterans General Hospital, Taiwan. The rate of overall infection was similar in both groups. However, subgroup analysis found that the fungal infection rate was significantly different, 41.7 and 17.1%, in the R-CHOP and CHOP groups, respectively, (P = 0.03). Univariate analysis identified the rituximab plus CHOP chemotherapy regimen (P = 0.03), age older than 80 years (P = 0.04), and bone marrow involvement (P = 0.04) as risk factors for development of fungal infection, whereas, multivariate regression analysis identified only rituximab plus CHOP and old age. Adding rituximab to the standard CHOP regimen in elderly DLBCL patients might increase the incidence of fungal infection especially in those older than 80 years old.