Objective: To assess the accuracy of self-reported financial conflict-of-interest (COI) disclosures in the New England Journal of Medicine (NEJM) and the Journal of the American Medical Association (JAMA) within the requisite disclosure period prior to article submission.

Design: Cross-sectional investigation.

Data sources: Original clinical-trial research articles published in NEJM (n=206) or JAMA (n=188) from 1 January 2017 to 31 December 2017; self-reported COI disclosure forms submitted to NEJM or JAMA with the authors' published articles; Open Payments website (from database inception; latest search: August 2019).

Main outcome measures: Financial data reported to Open Payments from 2014 to 2016 (a time period that included all subjects' requisite disclosure windows) were compared with self-reported disclosure forms submitted to the journals. Payments selected for analysis were defined by Open Payments as 'general payments.' Payment types were categorised as 'disclosed,' 'undisclosed,' 'indeterminate' or 'unrelated'.

Results: Thirty-one articles from NEJM and 31 articles from JAMA met inclusion criteria. The physician-authors (n=118) received a combined total of US$7.48 million. Of the 106 authors (89.8%) who received payments, 86 (81.1%) received undisclosed payments. The top 23 most highly compensated received US$6.32 million, of which US$3.00 million (47.6%) was undisclosed.

Conclusions: High payment amounts, as well as high proportions of undisclosed financial compensation, regardless of amount received, comprised potential COIs for two influential US medical journals. Further research is needed to explain why such high proportions of general payments were undisclosed and whether journals that rely on self-reported COI disclosure need to reconsider their policies.