Objectives To combat overcrowding in emergency departments, ambulance clinicians (ACs) are being encouraged to make on-site assessments regarding patients' need for conveyance to hospital, and this is creating new and challenging demands for ACs. This study aimed to describe ACs' experiences of assessing non-conveyed patients. Design A phenomenological interview study based on a reflective lifeworld research approach. Setting The target area for the study was Stockholm, Sweden, which has a population of approximately 2.3 million inhabitants. In this area, 73 ambulances perform approximately just over 200000 ambulance assignments annually, and approximately 25000 patients are non-conveyed each year. Informants 11 ACs. Methods In-depth open-ended interviews. Results ACs experience uncertainty regarding the accuracy of their assessments of non-conveyed patients. In particular, they fear conducting erroneous assessments that could harm patients. Avoiding hasty decisions is important for conducting safe patient assessments. Several challenging paradoxes were identified that complicate the non-conveyance situation, namely; responsibility, education and feedback paradoxes. The core of the responsibility paradox is that the increased responsibility associated with non-conveyance assessments is not accompanied with appropriate organisational support. Thus, frustration is experienced. The education paradox involves limited and inadequate non-conveyance education. This, in combination with limited support from non-conveyance guidelines, causes the clinical reality to be perceived as challenging and problematic. Finally, the feedback paradox relates to the obstruction of professional development as a result of an absence of learning possibilities after assessments. Additionally, ACs also described loneliness during non-conveyance situations. Conclusions This study suggests that, for ACs, performing non-conveyance assessments means experiencing a paradoxical professional existence. Despite these aggravating paradoxes, however, complex non-conveyance assessments continue to be performed and accompanied with limited organisational support. To create more favourable circumstances and, hopefully, safer assessments, further studies that focus on these paradoxes and non-conveyance are needed.