The concept of earlier diagnosis of amyotrophic lateral sclerosis (ALS) requires in-depth investigation of its benefits and consequences. First, how good must a treatment be before ALS is determined to be a treatable condition? Analogy with cancer therapy suggests that a good quality of life after treatment is an essential feature of a "good" therapy. Survival in some diseases may be prolonged without a significant improvement in the patient's quality of life. Neurologists need to be clear about what they are trying to achieve in prolonging survival and maintaining a good quality of life for their patients with ALS. Second, can early diagnosis extend apparent survival in the absence of a therapeutic intervention that significantly affects the disease process? Earlier diagnosis on the basis of confirmed clinical signs and earlier institution of therapy may lead to a perception of improved survival, which is greater in young ALS patients. Third, can early diagnosis provide a benefit through prolongation of the time the patient remains able to work? Any therapeutic intervention to slow the early stages of the disease would benefit patients who wanted to maintain their self-esteem by continuing to work. Finally, earlier diagnosis of ALS requires decisions to be made concerning the acceptable rate of misdiagnosis, which at present reaches 10% false-positive and up to 44% false-negative.