An ultrasound diagnosis apparatus includes a processing circuitry. The processing circuitry is configured to perform a two-dimensional ultrasound scan on a subject via an ultrasound probe. The processing circuitry is configured to generate two-dimensional ultrasound image data on the basis of echo data acquired by the two-dimensional ultrasound scan. The processing circuitry is configured to reconstruct two-dimensional medical image data from three-dimensional medical image data of the subject, on the basis of position information of the two-dimensional ultrasound image data in a first coordinate space specified from detected position information of the ultrasound probe and a correspondence relationship obtained in advance between a second coordinate space to which the three-dimensional medical image data belongs and the first coordinate space. The processing circuitry is configured to calculate a degree of similarity between the two-dimensional ultrasound image data and the two-dimensional medical image data every time a condition is satisfied.
