The present paradigm is that slow-growing and clinically unimportant lung cancers are very rare. Over the years, convincing evidence for their existence in significant numbers has been dismissed, but with computerized tomography scanning being increasingly common, their reality can no longer be denied. The time is now ripe for a paradigm shift--with consequences for screening as well as clinical practice in the future. The doubling time of the tumor is probably the most important factor for survival of the patient, and research on how to measure this figure is urgent. Age, smoking habits, and comorbidities of the patient are now the main factors when discussing treatment with the patient; once we can predict the behavior of the cancer, i.e., whether it is indolent or actually threatens the patient's life, we will be able to give better advice.