Salts and crystalline forms of 4-(4-{[2-(4-chlorophenyl)-4,4-dimethylcyclohex-1-en-1-yl]methyl}piperazin-1-yl)-N-({3-nitro-4-[(tetrahydro-2H-pyran-4-ylmethyl)amino]phenyl}-sulfonyl)-2-(1H-pyrrolo[2,3-b]pyridin-5-yloxy)benzamide are suitable active pharmaceutical ingredients for pharmaceutical compositions useful in treatment of a disease characterized by overexpression of one or more anti-apoptotic Bcl-2 family proteins, for example cancer.