There is limited prospective data on influenza infections in transplant recipients. However, influenza can be a significant cause of morbidity and mortality in some organ transplant populations. Reported attack rates have varied considerably and are likely due to differences in transplant populations, immunosuppression protocols, exposures, and type and virulence of circulating influenza viruses. Complications of influenza infection appear to be common in solid organ transplant (SOT) populations. There appears to be a relatively high rate of progression to viral pneumonia in some reports especially in lung transplant recipients. In one study of organ transplant recipients over a 10-year period, the rate of influenza infection ranged from 2.8 cases/1000 person years (liver transplant) to 41.8 cases/1000 person years (lung transplant). Complications including secondary bacterial pneumonia (17%) as well as extrapulmonary complications such as myocarditis, and myositis were observed. Influenza (and other respiratory viral infections) may lead to important immunological sequelae resulting in graft rejection and/or graft dysfunction. This may be secondary to activation of immunological mechanisms, including the upregulation of pro-inflammatory cytokines such as TNF-α, IL-6 and IL-8. Some studies of kidney and liver recipients have reported a high incidence of acute rejection following infection with influenza. However, while associations between influenza infection and rejection have been reported, a causal relationship has yet to be established.