BACKGROUND: Electronic cigarettes (e-cigarettes) are a frequently debated topic in public health. It is essential that clinical trials examining e-cigarettes are fully and accurately reported, especially given long-standing concerns about tobacco industry research. We assess the reporting of clinical trials sponsored by Juul Labs, the largest e-cigarette company in the USA, against accepted reporting standards. METHODS: We searched ClinicalTrials.gov for all trials sponsored by Juul Labs and determined those with registry data consistent with coverage by the Food and Drug Administration (FDA) Amendments Act 2007 (FDAAA). For trials with a primary completion date more than 1 year earlier, we searched ClinicalTrials.gov, the academic literature and a Juul-funded research database (JLI Science) for results. For located results, we compared reported outcomes with registered outcomes in line with Consolidated Standards of Reporting Trials (CONSORT) reporting guidelines. RESULTS: We located five registered trials sponsored by Juul Labs that appeared covered by the FDAAA 2007 in the public data. All five trials did not have results available on ClinicalTrials.gov. We found one publication and four poster presentations reporting results for four of the five covered trials outside of ClinicalTrials.gov. Of 61 specified outcomes, 28 were CONSORT compliant. Specific outcome reporting issues are detailed. DISCUSSION: Our findings raise substantial concerns regarding these trials. Clinicians, public health professionals, and the public cannot make informed choices about the benefits or hazards of e-cigarettes if the results of clinical trials are not completely and transparently reported. Clarification and potential enforcement of reporting laws may be required.