The hydraulic machine with radial cylinders (3, 4, 5, 6 and 7) comprises pistons (8) with radial stroke, arranged in contact with an outer cam (13) and coplanar with said group of cylinders, each equipped with a roller on the path (12) of said cam, and it has, in each piston (8), a rolling bearing (9, 10, 11); moreover, the roller (10) and rolling bearing (9, 10, 11) are small to allow, in the alternating motion of the piston (8), introduction steps of said roller in the respective liner of the cylinder (3, 4, 5, 6 and 7) . In each piston (21), an anti-friction ferrule, (23) is placed in contact with the pin (22) or with an interpositioned and coupled support element (25) for said roller (20); said ferrule being coupled with the inner diameter of the roller (20) itself. Finally, static and dynamic O-rings each consisting of a metal ring (28, 31) are mounted with interference in the coupling on the sealing diameter (D) and housed in a throat (29, 36) with slight axial clearance.