Consent transforms an otherwise illegitimate act into a legitimate one. To be valid, however, it must be adequately informed. The legal requirement is vague and provides little assistance in predicting when it will be satisfied. This is particularly so when a patient consents to a procedure and the physician subsequently varies one of the components of that procedure. Using three legal judgments and one General Medical Council (GMC) decision as a springboard, I have explored the concept of a medical procedure within the context of consent and developed a theoretical model to elucidate a more predictable and consistent informational requirement.