A mechanical reduction gear for a turbomachine, in particular for aircraft, this reduction gear comprising: - a sun gear having an axis of rotation, - a ring gear which extends around the sun gear, - planet gears which are meshed with the sun gear and the ring gear and which are held by a planet carrier, each planet gear having an axis of rotation and comprising a first toothing with a mean diameter for the meshing with the sun gear, and a second toothing with a mean diameter, which is different from the mean diameter of the first toothing, for the meshing with the ring gear, the second toothing comprising a series of upstream teeth (84d1) and a series of downstream teeth (84d2) located on either side of said plane and separated from each other by said first toothing, each of the planet gears being centred and guided in rotation about its axis with respect to the planet carrier by bearings (94a, 94b) located on either side of said plane, characterised in that the first toothing comprising a series of upstream teeth (82d1) and a series of downstream teeth (82d2) which are located on either side of a plane perpendicular to the axis of rotation of the sun gear and passing substantially through the middle of the planet gear, and in that said bearings (94a, 94b) are located on either side of said plane, an upstream bearing being interposed axially between the series of upstream teeth (84d1) of the second toothing and said plane, and a downstream bearing being interposed axially between the series of downstream teeth (84d2) of the second toothing and said plane. - a sun gear having an axis of rotation, - a ring gear which extends around the sun gear, - planet gears which are meshed with the sun gear and the ring gear and which are held by a planet carrier, each planet gear having an axis of rotation and comprising a first toothing with a mean diameter for the meshing with the sun gear, and a second toothing with a mean diameter, which is different from the mean diameter of the first toothing, for the meshing with the ring gear, the second toothing comprising a series of upstream teeth (84d1) and a series of downstream teeth (84d2) located on either side of said plane and separated from each other by said first toothing, each of the planet gears being centred and guided in rotation about its axis with respect to the planet carrier by bearings (94a, 94b) located on either side of said plane, characterised in that the first toothing comprising a series of upstream teeth (82d1) and a series of downstream teeth (82d2) which are located on either side of a plane perpendicular to the axis of rotation of the sun gear and passing substantially through the middle of the planet gear, and in that said bearings (94a, 94b) are located on either side of said plane, an upstream bearing being interposed axially between the series of upstream teeth (84d1) of the second toothing and said plane, and a downstream bearing being interposed axially between the series of downstream teeth (84d2) of the second toothing and said plane. the second toothing comprising a series of upstream teeth (84d1) and a series of downstream teeth (84d2) located on either side of said plane and separated from each other by said first toothing, each of the planet gears being centred and guided in rotation about its axis with respect to the planet carrier by bearings (94a, 94b) located on either side of said plane, characterised in that the first toothing comprising a series of upstream teeth (82d1) and a series of downstream teeth (82d2) which are located on either side of a plane perpendicular to the axis of rotation of the sun gear and passing substantially through the middle of the planet gear, and in that said bearings (94a, 94b) are located on either side of said plane, an upstream bearing being interposed axially between the series of upstream teeth (84d1) of the second toothing and said plane, and a downstream bearing being interposed axially between the series of downstream teeth (84d2) of the second toothing and said plane.