Ethical guidelines for behavior analysts state that functional assessment should be used before implementing treatment plans. In this paper, we discuss the ethical implications of this position using self-injurious behavior in people with developmental disabilities as a focus. Evidence is reviewed that suggests that treatment based on results of a functional assessment is likely to be more effective, less likely to be considered restrictive, more likely to be perceived as socially valid, and also focuses on principles of a constructional approach to behavior change. Alongside this generally positive evidence, there are ethical problems with the validity of some assessment methods, their potential lack of clarity, and the intensive resources required by a functional assessment. Effective, socially valid, and constructional interventions for self-injury might also be developed using preventative interventions. The balance of all of these ethical issues needs to be considered in the design of any treatments for self-injurious behavior.