AIM: Paediatricians using instant messaging phone apps for informal medical discussions poses ethical and legal risks. We filled a gap in the research, by assessing the use of apps and the possible risks. METHODS: A national, cross-sectional, questionnaire study was conducted in Israel from 11 August to 20 November 2019. The frequency of informal discussions, clinical details and recommendations were compared to the paediatricians' expertise and work settings. The discussions included work and private phones, consultation with the parents of patients and advice to the paediatricians' friends and families. RESULTS: The 305 paediatricians who responded had a median age of 37 (range 27-74) years: 42% were residents and 58% were specialists. The majority (99%) had carried out informal discussions using a messaging app in the last week and 65% had used them for 1-5 discussions. Specialists were more likely to use apps for more than 10 discussions per week than residents (24% vs. 5%, p <
0.001) and recommend treatment via apps (35% vs. 22%, p <
0.001). A third failed to provide disclaimers about the risks of app-based discussions. CONCLUSION: Using instant messaging apps for informal medical discussions was common, but ethical and legal aspects were not always fully considered.