Sectional-casing-design rotary pump in which the casing sections (8, 9) have a cylindrical outer casing and internal wall sections (12-15) in one piece therewith. The outer casing of at least one casing component (8, 9) consists of an outer continuous casing component (24, 25) and at least two separate inner casing components (19-22) with the appropriate internal wall sections (12-15). The outer and inner casing components are preferably firmly secured together, especially by shrink-fitting.