Clinical guidelines for severe behavioural problems (SBPs) in children have recently been developed in several European countries. However, questions emerged regarding their applicability to practice. Our study aimed to provide a first European insight into guidelines’ fitness-for-purpose by exploring mental health clinicians’ familiarity with, use and perceived value of guidelines for SBPs in children. Participants included 161 clinicians, primarily psychiatrists, from 24 countries. Clinicians completed a semi-structured qualitative questionnaire on existing SBPs guidelines and development of new guidelines where not available. Clinicians’ responses were mapped against academic experts’ perceptions on SBPs guidelines highlighted in a previous study (Gatej et al. in Eur Psychiatry 57:1–9, 2019). Under half of the clinicians reported being unaware of guidelines. Of these, 37.6% represented countries where guidelines were available according to experts. The remaining half of clinicians who were aware of guidelines on average reported being moderately familiar with their content, perceiving them as moderately useful and using them some of the time. Additionally, 60.8% clinicians agreed that SBPs guidelines need to be developed, as these would create a shared scientific knowledge base and common practice. Guideline improvements included taking a multifactorial approach, creating specific case recommendations, and dissemination efforts. The modest familiarity with and use of guidelines amongst practitioners may highlight guidelines poor fitness-for-purpose, or, alternatively, an underlying confusion around the meaning and purpose of guidelines. Moving forward, efforts should be directed at disseminating clearer definitions of guidelines, addressing existing challenges, and unifying efforts to further develop and audit application of international guidelines for SBPs.