Background Trial participation decisions are often influenced by expectations of potential benefit. Attention has focused on trial participation as a means of securing something seen as desirable, such as experimental treatment. In contrast, we consider a case in which one trial arm involved receiving less than usual care. We explore how this influenced participants’ decisions to participate. Methods Semi‐structured interviews with 29 women participating in a pilot trial comparing invasive urodynamic testing (typically normal care) to basic clinical assessment with non‐invasive tests, prior to surgical treatment for stress urinary incontinence. Analysis was based on the constant comparative method. Results Invasive tests were something many were aware of and worried about. Participants understood that trial participation meant they might avoid having these tests, and for about one‐third, this was the primary factor motivating participation. A further third mentioned they were not looking forward to tests (if allocated to them) or were lucky to have missed them (if allocated to basic clinical assessment). None of the women appeared to have discussed their desire to avoid having invasive tests with their clinicians. Conclusions In contrast to cases in which trial participation is motivated by the wish to secure an intervention not otherwise available, this study reports the opposite – trial participation as an opportunity to avoid having something regarded as undesirable. The option to decline a particular intervention should always be available, and care must be taken to ensure that potential participants are aware that trial participation is not the only possible means of avoidance.