Controversial aspects in prospective controlled trials in surgery can be detected at various stages in the course of this research work, such as in motivation, planning and performance as well as in assessment and evaluation of the results. Especially the introduction of control groups, randomization and "blindness" of patients, operators and doctors running the follow-up are subjects of a controversial discussion. Subthreshold arguments for defenders and eniers of the trial are taken from different theories of science, such as empirism and rationalism which are more effective in the daily routine work than expected. Provided that convincingly only therapeutic and diagnostic procedures are compared which were considered as equi-effective and reliable to the same extent according to the best and most complete knowledge available it is ethically justified to perform controlled randomized trials. It should, however, not be expected that they (always) produce differences between treatment of high degree of difference. The aim of the controlled trials is not the introduction of sensational novelties into medicine, but the abolition and prevention of unnecessary and unworthy modes.