Monitoring apparatus for monitoring a blood pressure of a subject , comprising: - a measurement unit comprising: an ultrasound transducer configured to emit ultrasound waves to a volume of the subject that includes a blood vessel and to receive ultrasound waves from said volume of the subject, and to provide first signal on the basis of ultrasound waves received from the volume of the subject; and a light source configured to emit light to the subject and a light sensor configured to detect emitted light received from the subject and to provide a second signal on the basis of the light received from the skin of the subject, and - a processing unit which is configured to: - determine a time of arrival of a cardiac pulse in the blood vessel based on the first signal, - determine a point in time when the cardiac pulse reaches the skin of the subject based on the second signal, - and determine a pulse transit time between the time of arrival of the cardiac pulse in the blood vessel and the point in time when the cardiac pulse reaches the skin of the subject; characterized in that the measurement unit has a common base layer to which the ultrasound transducer and the light sensor are attached, the common base layer having a pressure-inducing layer or one or more pressure transducer(s) arranged to, controlled by the processing unit , increase and decrease the pressure of the common base layer on the skin of the subject; and in that the processing unit is configured to determine the blood pressure based on the pulse transit time; and to provide optimum contact of the base layer to the skin of the subject by forming a feedback loop responsive to both the first signal and the second signal to determine and apply the pressure of the common base layer at a level such as to optimize the contact. - a measurement unit comprising: an ultrasound transducer configured to emit ultrasound waves to a volume of the subject that includes a blood vessel and to receive ultrasound waves from said volume of the subject, and to provide first signal on the basis of ultrasound waves received from the volume of the subject; and a light source configured to emit light to the subject and a light sensor configured to detect emitted light received from the subject and to provide a second signal on the basis of the light received from the skin of the subject, and - a processing unit which is configured to: - determine a time of arrival of a cardiac pulse in the blood vessel based on the first signal, - determine a point in time when the cardiac pulse reaches the skin of the subject based on the second signal, - and determine a pulse transit time between the time of arrival of the cardiac pulse in the blood vessel and the point in time when the cardiac pulse reaches the skin of the subject; - determine a time of arrival of a cardiac pulse in the blood vessel based on the first signal, - determine a point in time when the cardiac pulse reaches the skin of the subject based on the second signal, - and determine a pulse transit time between the time of arrival of the cardiac pulse in the blood vessel and the point in time when the cardiac pulse reaches the skin of the subject; <EOS>