Vitamin D deficiency is relatively common among older adults. Aim: To assess the knowledge and attitude of elderly patients regarding vitamin D deficiency. Design: Descriptive research design. Setting: The study was conducted in outpatient clinics at South Egypt Institute of Oncology -Assiut- Egypt. Sample: The total sample size was 148 during six months. The elderly patients were selected by purposive sample. Tools: Tool I: interview questionnaire was used for data collection. Part A: Patient Demographic Characteristics. Part B: Medical assessment. Tool II: Knowledge assessment questionnaire: to assess the elderly „knowledge about vitamin D deficiency among elderly. Tool III: Attitude assessment questionnaire: It was a Likert scale consisted of statements about the elderly patients. Results: it was observed that 68.2% of patients had poor score of knowledge, 23.6% had average score of knowledge and 8.1% had good knowledge score about vitamin D deficiency. Also, a positive correlation (r= 0.169) and highly significant difference (p. value = 0.017) between the elderly patient knowledge and attitude toward VitD deficiency. Conclusion and Recommendations: The present study answered the research questions that related to level of knowledge and attitude regarding vitamin D deficiency among elderly patients, and showed that there are some gaps in knowledge score about vitamin D. Further research can be conducted on larger sample involving control and experimental groups about vitamin D deficiency among elderly.