Secondary hypogammaglobulinemia is one of the factors responsible for the increased susceptibility to infection in patients with chronic lymphocytic leukemia (CLL). This study assessed the therapeutic results, concomitant medication and tolerance of administering 5% intravenous immunoglobulin, secondary immunodeficiency and recurrent serious bacterial infections. A single center, post-marketing, observational clinical study was performed on 10 patients with a variety of hematological malignancies (CLL, follicular non-Hodgkin lymphoma, IgM-secreting immunocytoma, IgA plasmacytoma and myelodysplastic syndrome/non-Hodgkin lymphoma) who had been infused with IVIG from June 1994 to May 2009. The clinical benefit of IVIG was assessed by comparing the incidence of bacterial infections before and after starting this therapy. Plasma immunoglobulin concentrations and relevant hematological variables were recorded. For safety assessment, adverse events were monitored. The standard IVIG dosage was approximately 0.35 g/kg body weight every 3–4 weeks. Most patients had normal IgG trough values of >600 mg/dL during the IVIG treatment period. The rate of bacterial infections was reduced from 2.4 per patient in the 3 months before IVIG to 0.7 (0–1.5) per patient per year during IVIG treatment. All patients received concomitant medication, mainly anticancer and anti-anemia therapy (100%). No serious adverse events related to IVIG were observed. The frequency of at least one minor adverse reaction was 1.44% (8/556 infusions). In conclusion, the investigated IVIG preparation was well tolerated and clinically beneficial in reducing the long term rate of serious bacterial infections in patients receiving concomitant treatment for malignant diseases.