Palliative Care (PC) takes into consideration all those cancer patients needing treatment for their symptoms throughout all stages of their illness The criteria for defining the patient population must be accurate and the characteristics of patients included in a clinical trial (CT) have to be well defined. The sample of patients has to be homogeneous and representative The following issues must be considered when determining patient population: 1. age, gender, type of cancer, educational level; 2. presence, intensity of symptom/s and other parameters under study; 3. the patient’s cognitive status for informed consent and use of assessment tools; 4. stage of disease (early, advanced, terminal); 5. simultaneous oncological and other therapies; 6. performance status (PS) and prognosis; 7. care setting (day hospital, hospice, home with multiprofessional care teams, nursing home, palliative care division in hospital, oncological ward). When considering and/or comparing patients in different care settings, PS and prognosis of the patients are essential. Sometimes patients are entered and studied as inpatients after which CTs are carried out on an out-patient basis: the patient’s clinical conditions are evaluated to establish any significant changes with respect to his/her baseline, if he/she are within easy reach of the ambulatory or can be contacted by phone in order to obtain the necessary data for the study in progress. In CTs when drugs with hepatic metabolism and/or renal secretion are studied, patients with renal and/or liver failure as well as epileptic patients who are currently receiving microsomial enzyme-inducing drugs are excluded. Moreover when pharmacokinetics are also studied, patients with malabsorption, altered distribution and metabolization or excretion are also excluded. It may be relevant to measure or assess the expectations of patients entering a CT. Furthermore the patient should feel free to leave the trial at any moment he/she wishes to do so.