SummaryBackgroundThe paradigm of early phase dose-finding trials has evolved in recent years. Innovative dose-finding designs and protocols which combine phases I and II are becoming more popular in health research. However, the quality of these trial protocols is unknown due to a lack of specific reporting guidelines. Here, we evaluated the reporting quality of dose-finding trial protocols.MethodsWe conducted a cross-sectional study of oncology and non-oncology early phase dose-finding trial protocols posted onClinicalTrials.govin 2017–2023. A checklist of items comprising: 1) the original 33-items from the SPIRIT 2013 Statement and 2) additional items unique to dose-finding trials were used to assess reporting quality. The primary endpoint was the overall proportion of adequately reported items. This study was registered with PROSPERO (no: CRD42022314572).FindingA total of 106 trial protocols were included in the study with the rule-based 3 + 3 being the most used trial design (39.6%). Eleven model-based and model-assisted designs were identified in oncology trials only (11/58, 19.0%). The overall proportion of adequately reported items was 65.1% (95%CI: 63.9–66.3%). However, the reporting quality of each individual item varied substantially (range 9.4%–100%). Oncology study protocols showed lower reporting quality than non-oncology. In the multivariable analysis, trials with larger sample sizes and industry funding were associated with higher proportions of adequately reported items (all p-values <0.05).InterpretationThe overall reporting quality of early phase dose-finding trial protocols is suboptimal (65.1%). There is a need for improved completeness and transparency in early phase dose-finding trial protocols to facilitate rigorous trial conduct, reproducibility and external review.FundingNone.