A patient's decision must be informed and free, and he/she must be competent either to consent to or refuse treatment. Rather than selecting a single standard of competency, a sliding scale is suggested that requires an increasingly more stringent standard as the consequences of the patient's decision embody more risk. The standard of competency to consent to or to refuse treatment depends on the dangerousness of the treatment decision. Three different standards are correlated with the psychiatric abnormalities that are most likely to undermine them. A model with guidelines for use is provided to aid the physician who is called on to make a determination of competency.