The extent to which a patient follows the advice of a doctor or other health professional, especially in respect of drug or other treatments. This is likely to be higher if the patient has shared in the decision to accept the offer of treatment and has been given every opportunity to understand both the condition and the basis for the proposed treatment. Assessment of a patient's compliance is a routine part of treatment review because failure to improve may be due to lack of compliance rather than failure of the medication itself or a worsening of the underlying illness.