Patients increasingly search for online information about clinical trials. Little is known about the quality and readability of the information in these databases. Therefore, the aim of this study was to assess the quality and readability of online information available to the public on phase I clinical cancer trials in Sweden, Denmark and Norway. A qualitative content analysis was made of 19 online trial descriptions from three public websites in Sweden, Denmark and Norway, and the readability of the documents was tested. Both the quality of the content and the readability scores were best for the Danish information. The Swedish texts were very short and were the least readable. Overall, the quality of the information was highly variable and nearly all the documents were misleading in part. Furthermore, the descriptions provided almost no information about possible adverse effects or disadvantages of study participation. This study highlights a communication problem and proposes new ways of presenting studies that are less suggestive of positive outcomes, arguing that we should be more careful to include information about adverse effects, and that the use of simple measures like readability testing can be useful as an indicator of text quality.