The variation in quality of the several thousand portal films submitted to the Quality Assurance Review Center (QARC) has been substantial. To ascertain the nature and severity of this problem, a detailed study of “whole brain” portal films which were taken at 23 different radiotherapy departments for patients entered on three national leukemia studies was performed. Each film was analyzed in two ways: (a) independent subjective evaluation by four experienced radiotherapists and (b) measurement of objective parameters. Scores from 416 evaluations together with measured parameters were stored in a data base system for easy statistical manipulation. The dependence of perceived film quality on these objective parameters has been correlated and is the subject of this report.