The present invention relates to novel amorphous and crystalline forms of efavirenz, processes for their preparation and pharmaceutical compositions containing them. In accordance with the present invention efavirenz crude is dissolved in acetone at 25° C.-30° C., the solution is slowly added to water for 30 minutes at 0° C.-5° C., stirred for 1 hour at the same temperature, the separated solid is filtered, washed with water and dried at 55° C.-60° C. for 5 hours to give amorphous efavirenz.