Disclosed is a crystalline form of (S)-1-(4-Chloro-phenyl)-7-isopropoxy-6-methoxy-2-(4-{ methyl-[4-(4-methyl-3-oxo-piperazin-1-yl)-trans-cyclohexylmethyl]-amino} -phenyl)-1,4-dihydro-2H-isoquinolin-3-one (see abstract figure) sulfate salt, which may be the bisulfate salt. Also disclosed are pharmaceutical compositions containing this crystalline form and methods of treatment of a disease or disorder associated with the activity of MDM2 and/or MDM4. These can include tumours and cancers.
