PURPOSE Company-reported payments from the Open Payments database (OP) have been compared with self-disclosed financial relationships made by physician authors. Discrepancies have been viewed as under-reporting of financial relationships. Our goal was to perform a systematic comparison to determine sources of discordance between company-reported and self-reported financial relationships. METHODS Financial disclosures reported by 163 authors and presenters who published in Journal of Clinical Oncology or who presented an abstract at the ASCO 2018 Annual Meeting were obtained and matched to payment data in OP. Categories included ownership, research, consulting/services, honoraria, expenses, royalty/patent/intellectual property, and other disclosures. Measures of concordance and discordance were calculated on the basis of matches on both company and category of disclosure and matches on company. Results are reported overall and within certain categories of disclosures. RESULTS Overall concordance between disclosures to ASCO and payments in OP was 16% for company and category matching and 24% for matching on the basis of company only. Authors tended to report more disclosures for research and consulting to ASCO than appear in OP. Expense disclosures were more frequently reported in OP than to ASCO. No payments were categorized as ownership in OP, but 35 authors/presenters disclosed ownership (including stock) to ASCO. CONCLUSION Our results reveal substantial discordance between self-reported and company-reported financial relationships for authors who report clinical oncology research. These findings support the calls for development of standardized disclosure policies across medicine.