Studies on the incidence of bacteraemia following endoscopic injection sclerotherapy produce equivocal results. Accordingly, we performed a prospective study in 24 patients who underwent a total of 40 sclerotherapy sessions. Blood was drawn before, during, and 5 minutes, 30 minutes, 3 hours and 24 hours after sclerotherapy. Transient bacteraemia (mostly during and 5 minutes after sclerotherapy) was detected in 21 (53%) procedures. The bacteraemic events bore no relation to febrile episodes. The most frequently isolated microorganisms were alpha-haemolytic Streptococcus spp. and coagulase-negative Staphylococcus spp.. We conclude that injection sclerotherapy is associated with a high incidence of bacteraemia which, however, in most cases is transient and does not lead to septic disease.