Which proxy-reported outcome measures have been developed for use with children aged 6 years and younger to assess asthma symptoms, asthma control, and asthma-specific health-related quality of life, and do these questionnaires' measurement properties support their use as end-points in clinical trials? A two-phase literature search was conducted: 1) studies describing relevant questionnaires were identified, and the questionnaires were assessed against predefined criteria; 2) studies providing information on the measurement properties of questionnaires meeting the predefined inclusion criteria were identified. Literature sources included PubMed and EMBASE databases, scientific conference proceedings, a clinical trial registry, and a quality of life instrument database. The initial search of literature databases and conference abstracts identified 631 records. 20 paediatric asthma proxy-reported outcome instruments were identified; seven met the inclusion criteria: Childhood Asthma Control Test, Control de Asma en Niños Questionnaire, Pediatric Asthma Caregiver Diary, Pediatric Asthma Control Tool, PedsQL 3.0 Short-Form 22 Asthma Module, PedsQL Asthma Symptoms Scale, and Test for Respiratory and Asthma Control in Kids. Three proxy-reported outcome instruments were considered suitable for use as end-points in paediatric asthma clinical trials; the Pediatric Asthma Caregiver Diary possesses the strongest measurement properties of the three.