Title: Prevalence and characteristics of promissory conference abstracts, i.e. abstracts without results, accepted at Cochrane Colloquia 1994-2020 Background: Conference abstract summarizes in written form a research topic that will be presented at a conference. They are published in the conference abstract book. An abstract describing a research study can sometimes present only of a plan of the study, without any results, along with a note that the results will be presented at a conference. Such an abstract is referred to as promissory abstract. Aim: To analyze frequency and characteristics of promissory conference abstracts, i.e. abstracts submitted without results, accepted at 25 Cochrane Colloquia in the period of 26 years. Methods: Conference abstracts (N=8297) accepted at 25 Cochrane Colloquia, organized in the period 1994-2020, which were publicly available on the web site of the Cochrane Library, were analyzed. All abstracts were screened in order to identify promissory abstracts. Characteristics of promissory abstracts were extracted. Results: Abstracts that were duplicate, or in which the text was partially or entirely missing, (N=89) were excluded. Among the remaining 8203 abstracts there were 717 (8.7%) promissory abstracts. Among 717 promissory abstracts, 475 (66%) were accepted as poster presentations, 241 (34%) as oral presentations and 1 was accepted as a workshop. The majority of promissory abstracts listed from 1 to 6 authors (N=558; 78%). In 245 (34%) promissory abstracts affiliations of authors were not reported. In the remaining 472 promissory abstracts, authors were affiliated with a total of 56 different countries. The authors were most commonly affiliated with the UK (N=472; 36%) and Canada (N=123; 26%). There were 512 (71%) promissory abstracts in which study design was not reported. In the remaining 205 promissory abstracts, the authors used 75 different descriptors for their study designs. The most common self-reported study designs of promissory abstracts were systematic review (N=58; 28%) and scoping review (N=12; 5.9%). Conclusion: Promissory abstracts were commonly submitted to Cochrane Colloquia. Such abstracts have no informative value for the readers, and they are detrimental in terms of dissemination of new knowledge presented at a conference. Conference organizers could ask the authors to update the abstract results subsequently.