Although varicella is most often a benign and self-limited disease of childhood, it can be associated with a variety of serious and potential lethal complications. Especially, the incidence of severe infectious complications caused by group A streptococci has been increasing over the last years. We report the case of a previously healthy young boy with an aortic bicuspidy who developed a varicella complicated by endocarditis due to group A streptococcus, and a haemophagocytic syndrome. A favorable outcome was obtained after an early valvular replacement and 6 weeks of intravenous antibiotics.