Trials often do not succeed in including as many patients as anticipated beforehand. The aim of this paper was to describe why we were not able to include more than a few patients in our randomized controlled treatment trial on the effectiveness of bracing patients with idiopathic scoliosis, and to describe which lessons can be learnt. A pilot study on the willingness to participate in such a trial was conducted amongst 21 patients and their parents. A description of how we prepared and designed this trial, the problems we faced and how we tried to improve the inclusion are given. A total of four patients were included, and 14 refused to participate in an 18-month period. There were a lot less eligible patients than anticipated (40 instead of 100 per year), and the patients' participation rate was much lower than we had found in our pilot study (21% instead of 70%). The trial failed to include more than a few patients because of an overestimation of the number of eligible patients and because a lot less eligible patients were willing to participate compared to our pilot study. One reason for a low participation rate could be that this trial evaluated a frequently used existing treatment instead of a new treatment, and patients and parents might be afraid of not being treated (despite an intensive secure system for the control arm).