An apparatus (100) for assessing the condition of the bone tissue in a patient's bone region (21), comprising an ultrasound device (11) that has a means for transmitting/receiving ultrasounds along a plurality of ultrasound propagation lines (15|) arranged for achieving the bone region (21), and for receiving in response from the bone region (21) a plurality of raw reflected ultrasound signals (36, 38); a means for generating an ultrasound signal, a sonographic image formation means for forming a sonographic image (29) of the bone region (21), starting from the raw reflected ultrasound signals (36, 38); a means for extracting at least one frequency spectrum (43, 44, 47, 48) starting from at least one part of said plurality of raw reflected ultrasound signals (36,38) coming from corresponding points (34) of the bone region (21), each having a plurality of harmonic components wherein to each frequency (v) of the frequency range an intensity is associated (A) of a portion of one of the raw reflected ultrasound signals; a means for comparing (24) at least one frequency spectrum (43, 44, 47, 48) with at least one reference spectrum (52) that is associated with at least one healthy and/or pathological subject, and for calculating a diagnostic parameter according to this comparison. The apparatus allows therefore an approach guided by a sonographic image, unlike what happens in ultrasound bone densitometry devices of the prior art, which use ultrasound beams for measuring their attenuation, without any reference to the detail of the bone region. The ultrasound beams can run over the bone network according to modes that depend on the structure of the network, and allow therefore to obtain information of this structure, as well as bone densitometry data.