Background: Outcome reporting bias refers to the selective reporting of some outcomes but not others in trial publications. Such bias has been recognised as a potential threat to the validity of any meta-analysis (Song et al., 2000; Copas and Jackson, 2004; Olsen et al., 2007; Williamson and Gamble, 2007). Without complete reporting of research findings, any attempt to recommend a treatment is likely to be based on biased information (Melander, 2003). Little research, however, has been undertaken to understand the process of reporting research findings from the viewpoint or situation of the researcher. To our knowledge, no qualitative research has assessed researchers’ understanding of the potential sources of bias in the analysis and reporting of research findings. Interviewing trialists as part of the ORBIT project (UK MRC G0500952) provided a unique opportunity to gain insight into researchers’ understanding of issues around reporting bias. Objectives: To further our understanding of the processes resulting in selective outcome reporting through interviews with clinical trialists. Methods: Semi-structured qualitative interviews conducted by telephone with trialists identified from two separate sources (Cochrane reviews and research registers) and three groups (trials with outcome reporting bias, trials without outcome reporting bias, cohort of trials identified from research register). It is anticipated that we will conduct a maximum of 80 interviews. The interview schedule deals with four broad topic areas: specific questions relating to outcome reporting bias; general questions relating to the writing and getting the trial paper published; general questions relating to publication bias more generally; and questions regarding understanding of the research process and reporting of outcomes. Results: Initial analysis suggests that few trialists are aware of this potential source of bias and of how to prevent it occurring. Conclusions: This study will provide an understanding of the processes resulting in outcome reporting bias and of what will help to minimise such problems in reporting of future trials.