PURPOSE This study was conducted to assess the readability of informed consent forms that describe clinical oncology protocols. METHODS One hundred thirty-seven consent forms from 88 protocols that accrued patients at The Johns Hopkins Oncology Center were quantitatively analyzed. These included 58 of 99 (59%) institutional protocols approved by The Johns Hopkins Oncology Center's Clinical Research Committee and the Institutional Review Board (IRB) over a 2-year period, and 30 active Eastern Cooperative Oncology Group (ECOG), Radiation Therapy Oncology Group (RTOG), and Pediatric Oncology Group (POG) trials. The consent forms described phase I (17%), phase I/II (36%), phase III (29%), and nontherapeutic (18%) studies. Each was optically scanned, checked for accuracy, and analyzed using readability software. The following three readability indices were obtained for each consent form: the Flesch Reading Ease Score, and grade level readability as determined by the Flesch-Kincaid Formula and the Gunning Fog Index. RESULTS The mean +/- SD Flesch Reading Ease Score for the consent forms was 52.6 +/- 8.7 (range, 33 to 78). The mean grade level was 11.1 +/- 1.67 (range, 6 to 14) using the Flesch-Kincaid Formula and 14.1 +/- 1.8 (range, 8 to 17) using the Gunning Fog Index. Readability at or below an eighth-grade level was found in 6% of the consent forms using the Flesch-Kincaid Formula and in 1% using the Gunning Fog Index. Readability was similar for consent forms that described institutional, cooperative group, and phase I, II, and III protocols. CONCLUSION Consent forms from clinical oncology protocols are written at a level that is difficult for most patients to read, despite national, cooperative group, institutional, and departmental review. The consent process, which is crucial to clinical research, should be strengthened by improving the readability of the consent forms.