Influenza is a potentially serious infection after hematopoietic SCT (HSCT). Vaccination is the main prophylactic approach in individuals at an increased risk for severe influenza disease or post-influenza complications. No controlled study on the efficacy of influenza vaccination has been performed in HSCT recipients and also studies evaluating the antibody response are limited by their small sizes and by that vaccinations have been performed at varying times after HSCT. The reports show that serological response rates are lower in HSCT patients than in healthy individuals. However, patients receiving influenza vaccine at 6 months or later after HSCT have a lower risk for virological confirmed influenza. The documentation for efficacy if patients are vaccinated earlier than 6 months after HSCT is mostly lacking but it has been shown that T-cell responses can be elicited after vaccination. Therefore, currently available recommendations suggest starting earlier when the risk for influenza is high, especially during ongoing community outbreaks. Two vaccine doses are recommended in children below the age of 9 years, who have not been previously vaccinated against influenza. Vaccination of family members, close contacts and health-care workers is recommended.