The range of diseases in which intravenous immunoglobulin (IVIG) is effective has expanded significantly since its initial use in primary antibody deficiency. This biological medicine must comply with three conditions: therapeutic efficacy, clinical tolerance and viral safety. Factors relevant to the viral safety of IVIG include: effective use of donor exclusion criteria, screening of donations in order to exclude potentially infectious donations, testing of plasma pools for evidence of viral infection, validated steps for removal and/or inactivation of potentially present infectious agents, equipment cleaning, traceability of lots, and post-marketing follow-up of patients. Variables potentially affecting the risk and intensity of adverse events associated with administration of IVIG include: patient age, underlying condition, dose, concentration, IgA content, stabilizing agent and rate of infusion. Mild adverse reactions (headache, flushing, low backache, nausea) are often associated with a fast infusion rate, and respond rapidly on slowing the infusion. Very rare serious and potentially fatal side effects include: anaphylactic reactions, aseptic meningitis, acute renal failure, and thrombotic complications. Many of these serious adverse reactions have occurred in patients who had significant risk factors or underlying disease states. Clinicians should pay close attention to patient selection and consider the potential risk/benefit ratio versus alternate therapies.