Abstract Introduction Knowledge of genetics and nutritional genomics is important for dietitians in the prevention and management of disease. The present study aimed to analyse data from a nationwide postal questionnaire survey in order to investigate the factors associated with knowledge of genetics and nutritional genomics among dietitians in the UK. Methods A nationwide postal questionnaire survey was conducted in a random sample of 600 dietitians in the UK. The questionnaire measured dietitians’ knowledge using 12 multiple choice questions relating to genetics and nutritional genomics. Factors that may impact upon such knowledge were also recorded. Knowledge scores were calculated and compared between dietitians using comparative statistics and univariate analysis of variance. Results A total of 389 (64.8%) usable questionnaires were returned. Overall, the mean ± SD total knowledge score was low at 41 ± 19%. Highest qualification (F2,372 = 9.1, P <0.001), the genetics content of university education (F2,372 = 7.1, P =0.001) and reading literature or attending a conference relating to genetics or nutritional genomics within the last year (F1,372 = 11.9, P =0.001) were all associated with higher total knowledge scores. Conclusion Knowledge of genetics and nutritional genomics among dietitians is currently low, and better knowledge is associated with exposure to these in university education and continuing professional development.