This study aimed to elucidate the relationship between maternal psychosocial factors related to dietary adherence and growth outcomes in their children with cystic fibrosis (CF). Twenty-five children with CF and mild lung disease, aged 7-12 years, were weighed and measured and completed detailed food records. Mothers completed questionnaires that measured general nutritional knowledge, nutritional knowledge specific to CF, coping strategies, dieting behaviors, self-efficacy about the ability to provide the correct diet, and attitudes and beliefs about CF. Of the cohort, only 16% adhered to the dietary recommendations. Dietary adherence was positively correlated with weight. Maternal nutritional knowledge specific to CF significantly predicted children's dietary adherence score. There was a significant negative correlation between the child's weight and mothers who were dieting successfully. Other psychosocial factors assessed were not related to dietary adherence. Improving the mother's knowledge about nutritional needs in CF appears worthwhile and may have an impact on growth.