Objective: The present study aimed to evaluate the knowledge and practices of public-sector primary-care health professionals and final-year students regarding the role of nutrition, physical activity and smoking cessation (lifestyle modification) in the management of chronic diseases of lifestyle within the public healthcare sector. Design: A comparative cross-sectional descriptive quantitative study was conducted in thirty primary health-care facilities and four tertiary institutions offering medical and/or nursing programmes in Cape Town in the Western Cape Metropole. Stratified random sampling, based on geographical location, was used to select the health facilities while convenience sampling was used to select students at the tertiary institutions. A validated self-administered knowledge test was used to obtain data from the health professionals. Results: Differential lifestyle modification knowledge exists among both health professionals and students, with less than 10 % achieving the desired scores of 80 % or higher. The majority of health professionals seem to be promoting the theoretical concepts of lifestyle modification but experience difficulty in providing practical advice to patients. Of the health professionals evaluated, doctors appeared to have the best knowledge of lifestyle modification. Lack of time, lack of patient adherence and language barriers were given as the main barriers to providing lifestyle counselling. Conclusions: The undergraduate curricula of medical and nursing students should include sufficient training on lifestyle modification, particularly practical advice on diet, physical activity and smoking cessation. Health professionals working at primary health-care facilities should be updated by providing lifestyle modification education as part of continuing medical education.