Coagulation disorder associated with essential thrombocythemia may exacerbate the prothrombotic state physiologically occurring during pregnancy. We report a case of a severe postpartum haemorrhage in a 35-year-old woman previously diagnosed with essential thrombocythemia and carrying the somatic calreticulin mutation. She was referred to our Thrombosis and Haemostasis Unit for pregnancy management. A treatment with low-dose aspirin was prescribed until the labour started, as the platelets count raised above 1000 × 10/l. At the time of bleeding, no residual placenta was detected at the revision of the uterine cavity.Although the postpartum is a high-risk period for thrombotic events, we have to carefully evaluate in women with essential thrombocythemia the likelihood of developing a hemorrhagic complication.