The present invention relates to improved processes for preparing 3-(4-amino-1-oxo-1,3-dihydro-isoindol-2-yl)-piperidine-2,6-dione (I) (lenalidomide) and its intermediate 3-(1-oxo-4-nitro-1,3-dihydro-isoindol-2-yl)-piperidine-2,6-dione. The present invention further relates to improved processes for preparing lenalidomide crystalline form A, use of said crystalline form A as an active pharmaceutical ingredient or as an intermediate in the preparation of further crystalline or amorphous forms of lenalidomide, compositions comprising lenalidomide crystalline form A and their use in the treatment of disease.