A method of estimating the distribution of bone mineral density in at least one portion of a person's skeleton. The method includes generating a geometrical representation of the portion of the skeleton; a geometrical representation in three dimensions of at least one portion of the outline of the person; and first and second X-ray images; and using software to estimate: a value for the thickness of soft tissue through which the given X-ray has passed; an attenuation coefficient of the soft tissues that have been passed through; a value for the thickness of bone tissue through which the given X-ray has passed; and using the thickness value for the soft tissue through which the given X-ray has passed, and a value for the attenuation of the given X-ray due to the thickness of the bone tissue through which it has passed, the software estimates a value representative of the bone mineral density of the bone tissues through which the given X-ray has passed.