A stable micronised monoclinic form of asenapine maleate is described, which comprises 5% by weight or less of orthorhombic form or any other crystalline form of asenapine maleate, wherein the asenapine maleate has a particle size distribution characterised by a d90 equal to or below 40 &mum. Processes for preparing the stable micronised monoclinic form of asenapine maleate are also described. Formula (I).
