To help the understanding of the physical behavior of Ca_1-xY_xMnO₃, its phase diagram in the whole x concentration range was investigated taking into account the stability of phases and the possible coexistence of different structural phases. By careful analysis of powder X-ray diffraction (XRD) patterns, we were able to observe the following phase diagram: (i) Orthorhombic phases were detected both in the region of 0 < x < 0.25 (O type phase with Ca site twelve fold coordinated) and in the region of 0.5 < x < 0.75 (O′ type phase with Ca site ninefold coordinated). (ii) Phase segregation for 0.25 < x < 0.5 and for x > 0.75 that have not been reported previously, hexagonal YMnO₃ segregates as a separate phase for x > 0.75, and for 0.25 < x < 0.5 the coexistence of Ca_0.75Y_0.25MnO₃ (O) and Ca_0.5Y_0.5MnO₃ (O′) have to be included in the refinement for it to converge.