Background: Impeccable assessment of symptoms is central to palliative care (PC) practice. Objectives: The study objectives are (1) to test the validity of the Arabic Questionnaire for Symptom Assessment (AQSA) as a self-administered (SA) tool for assessing the severity of the listed symptoms among PC patients and (2) to test the validity of AQSA when completed by a proxy. Methods: The AQSA is a tool for assessing the severity of 11 symptoms in addition to the overall suffering experience on a 0 to 10 numeric scale. Symptom scores on the SA AQSA were compared to scores obtained through interviews with patients. The same procedure was repeated with patients' sitters to explore the validity of using the tool for symptom assessment by proxy. Results: The study involved 107 pairs (a patient and a sitter, each) with a mean age of 46.3 years (females 59.8%) for patients and 35.9 years (females 65.7%) for sitters. The correlation coefficient (r) for agreement between SA and interview-based (IB) scores for patients ranged from .65 (P < .0001) for drowsiness to .86 (P < .0001) for pain. The SA AQSA showed positive correlation between sitters' and patients' scores, with r ranging from .28 (P = .004) for depression to .62 (P .0001) for vomiting. Conclusions: The strong positive correlation between SA and IB AQSA indicates that the former is a valid tool. When the SA AQSA is used by proxy, it showed moderate to strong positive correlation with patients' actual scores for most of the symptoms.