This study’s primary objective was to establish differences in beliefs about medicines, levels of asthma-related anxiety and diet and exercise behaviours between parents of children with well controlled and poorly controlled asthma. Secondary objectives were to explore how asthma control might shape relationships between parental cognitions and parenting practices concerning paediatric asthma. Parents of children with asthma aged 10–16 years ( N = 310) completed standardised questionnaires measuring beliefs about medicines, parental asthma-related anxiety, parenting attitudes towards child activity, parental feeding and asthma control. Parents of children with poorly controlled asthma reported significantly greater asthma medication necessity and concern, asthma-related anxiety, control of child activity, pressure to exercise and unhealthy feeding practices. Moderation analyses indicated that the relationship between parental concern about asthma medicine and parental control of child activity was strongest in children with poorly controlled asthma. Also, the relationship between parental asthma-related anxiety and use of food to regulate child emotion was only significant when asthma was poorly controlled. Parental beliefs about asthma medicines and asthma-related anxiety may indirectly influence asthma outcomes through unhealthy parenting practices around exercise and diet. Eliciting and understanding parents’ perceptions of asthma medications and anxiety may facilitate personalised interventions to improve asthma control.