A pro-apoptotic solid dispersion comprises, in essentially non-crystalline form, a Bcl-2 family protein inhibitory compound of Formula I as defined herein, dispersed in a solid matrix that comprises (a) a pharmaceutically acceptable water-soluble polymeric carrier and (b) a pharmaceutically acceptable surfactant. A process for preparing such a solid dispersion comprises subjecting to elevated temperature the compound of Formula I, the water-soluble polymeric carrier and the surfactant, to provide an extrudable semi-solid mixture; extruding the semi-solid mixture; and cooling the resulting extrudate to provide a solid matrix comprising the polymeric carrier and the surfactant and having the compound dispersed in essentially non-crystalline form therein. The solid dispersion is suitable for oral administration to a subject in need thereof for treatment of a disease characterized by overexpression of one or more anti-apoptotic Bcl-2 family proteins, for example cancer or an immune or autoimmune disease.