An implantable device (100, 700, 800) for controlling the internal circumference of an anatomic orifice or lumen, comprising: an annular ring (115, 705, 805); means (500, 646, 710) by which said annular ring can be fastened to the tissue around an anatomic orifice or lumen; means (20,130, 725, 825) associated with said annular ring for permitting adjustment of the circumference of said annular ring from a first circumference to a second circumference; and means (20,130, 720, 820) associated with said annular ring for maintaining said ring in said first circumference and, upon said annular ring being adjusted to said second circumference, for maintaining said annular ring in said second circumference; whereby the circumference of said anatomic orifice or lumen can be adjusted by adjusting the circumference of said annular ring from said first circumference to said second circumference the means (725, 825) associated with said annular ring for permitting adjustment of the circumference of said annular ring from a first circumference to a second circumference comprises an adjustable section on the annular ring, wherein the adjustable section is provided with a series of adjustment stops and wherein the means (725, 825) further comprise an engaging means comprising a mechanism (750, 755:850, 855) having a housing supporting and containing a mechanical worm characterised in a first geared head attached to the mechanical worm which mates with a second geared head, wherein the second geared head is attached to an adjustment stem, such that torsion imparted to the adjustment means by the operator will result in the turning of the adjustment stem and second geared head allowing motion of the first geared head and worm, which creates motion of the adjustable implant section as the worm engages with the series of adjustment stops. an annular ring (115, 705, 805); means (500, 646, 710) by which said annular ring can be fastened to the tissue around an anatomic orifice or lumen; means (20,130, 725, 825) associated with said annular ring for permitting adjustment of the circumference of said annular ring from a first circumference to a second circumference; and means (20,130, 720, 820) associated with said annular ring for maintaining said ring in said first circumference and, upon said annular ring being adjusted to said second circumference, for maintaining said annular ring in said second circumference; whereby the circumference of said anatomic orifice or lumen can be adjusted by adjusting the circumference of said annular ring from said first circumference to said second circumference the means (725, 825) associated with said annular ring for permitting adjustment of the circumference of said annular ring from a first circumference to a second circumference comprises an adjustable section on the annular ring, wherein the adjustable section is provided with a series of adjustment stops and wherein the means (725, 825) further comprise an engaging means comprising a mechanism (750, 755:850, 855) having a housing supporting and containing a mechanical worm characterised in a first geared head attached to the mechanical worm which mates with a second geared head, wherein the second geared head is attached to an adjustment stem, such that torsion imparted to the adjustment means by the operator will result in the turning of the adjustment stem and second geared head allowing motion of the first geared head and worm, which creates motion of the adjustable implant section as the worm engages with the series of adjustment stops.