Background: The International Committee of Medical Journal Editors (ICMJE) requires trials submitted for publication to be registered before enrolment of the first participant; however, there is ambiguity around the definition of recruitment and in anchoring the trial start date, end date, recruitment and enrolment, temporally to trial processes. There is potential for variation in how recruitment is reported and understood in trial protocols and trial reports. We report on Phase 1 of a concept analysis of ‘trial recruitment’ and develop a preliminary operational definition of ‘trial recruitment’. Methods: A concept analysis using the hybrid model. We searched randomised and non-randomised trial reports published between January 2018 and June 2019. Included studies were sourced from the five top journals in the category of medicine with the highest impact factor. We examined how recruitment was defined temporally to four time points; screening, consent, randomisation, and allocation. Results: Of the 150 trial reports analysed, over half did not identify a clear time point of when recruitment took place in relation to any of screening/consent/randomisation/allocation. The majority of the assessed trials provided a time frame in relation to the trial (i.e. start/end date), the process that this time frame referred to differed between studies. There was variation across studies in the terminology used to describe entry to the trial and often multiple terms were used interchangeably. Conclusion: There is ambiguity around temporal descriptions of ‘trial recruitment’ in health care journals. Informed by the findings of Phase 1, we developed a preliminary temporal operational definition of trial recruitment based on i) trial recruitment of an individual or cluster and ii) the trial recruitment period. In Phase 2 this definition will be discussed in focus groups with healthcare workers involved in designing/implementing/reporting on trials; to contribute to the final phase (analytical phase) of this concept analysis.