A breast implant system comprises at least one first element (1) and at least one second element (2) for implantation in the patient's body so as to form part of a breast implant (10). The first element is displaceable relative to the second element, when implanted in the patient's breast, so as to change the outer shape of the breast implant. Preferably, the elements are contained in a casing (12, 13) with a flexible outer shape. More preferably, a reservoir (R) comprising a lubricating fluid is connected to the casing so as to allow lubricating fluid to be supplied to, and removed from, the casing, in order to reduce surface friction between adjacent elements, and/or between the casing and the elements, before the shape of the breast implant is changed by relative displacement of the first and second elements.
