The present invention relates to a process for the preparation of crystalline non-hygroscopic form H1 of efavirenz, and pharmaceutical compositions containing it. In accordance with the present invention efavirenz was dissolved in acetone at 25° C.-30° C., the solution was slowly added to water at 0° C.-5° C., the separated solid was filtered, washed with mixture of acetone and water and dried at 25° C.-35° C. under below 65% relative humidity for 18 hours to give crystalline non-hygroscopic efavirenz form H1.