In previous studies without maintenance therapy, median overall survival (OS) for performance status (PS) 0-1 patients has been approximately 9 months, corresponding to 6 months from randomization in this study. We consider an improvement in overall survival of two months to be the minimum difference that will lead to routine use of maintenance pemetrexed in Norway. To demonstrate an improvement in median overall survival from 6 to 8 months with an α =0.05 and β =0.20, 198 evaluable patients are required on each arm. We expect a drop-out rate of maximum 10 %, and therefore intend to randomize a total of 436 patients (PS 0-1) - of which we expect 150 to be 70 years or older.