The present invention concerns a method and a system for measuring non-invasively a blood pressure of a patient. The method comprises the steps of: determining (1603) a mechanical heart beat starting time point from an impedance cardiogram signal, detecting (1605) a heart beat pulse arrival time at a peripheral site of the patient, calculating (1607) a pulse wave transit time from the heart to the peripheral site by utilizing said mechanical starting point of the heart beat and said heart beat pulse arrival time,

• calculating (1609) an estimate of the blood pressure of the patient from said pulse wave transit time.