Abstract: Herein described is a frame (10) for a fluid machine of the reciprocating type. The frame (10) bears one or more cylinders (12) moving inside each of which, with a reciprocating movement, is a piston operated by a crankshaft (14). The frame (10) is made up of one or more modules (20) of the same size and shape, within each one of the modules (20) being provided a single chamber (16) adapted to accommodate the crank mechanisms of each single cylinder (12). Each module (20) is further provided with a pair of opposite side walls (22, 24) and with one or more fixing means (26) which allow rigid coupling to each other, adjacently arranging their respective side walls (22, 24), of two or more of the identical modules (20) for providing a frame (10) for fluid machines provided with two or more cylinders (12).