The ambulance service provides vital front line mental healthcare for young people in crisis, but there is a lack of evidence to guide best practice in this area. The lived experiences of service users can offer important insights to guide service development, therefore we carried out a qualitative evaluation of care provided by the ambulance service to young people experiencing a mental health-related emergency. Ten participants aged 16-25 years who had used the ambulance service due to a mental health crisis within the past 2 years were interviewed about their experiences and view of the care they received. Interviews were transcribed verbatim and interpretative phenomenological analysis used to explore participants' individual narratives and identify recurrent themes. A theme of inconsistent quality of care was evident in all participants' accounts. Contributing to this superordinate theme were six recurrent themes: positive qualities of individual ambulance clinicians, ambivalence about seeking care, the importance of retaining agency, need for mental health training for ambulance clinicians, need for inter-service collaboration and favourable comparison of the ambulance service to other services. We identified some examples of good practice, including person-centred care, respect for patient autonomy and attending to physical health needs. However, our findings suggest the quality of ambulance service mental healthcare is not yet sufficiently consistent. In the absence of mandatory high-quality mental health training and evidence-based protocols, the quality of care appears largely dependent on the qualities and experience of individual ambulance clinicians.