Clinical trials in paediatric cancer continue to be a key factor in progress toward better treatment and prognosis. Paediatricians and family physicians may be asked by patients and families for their advice regarding participation in such trials. The significant advances in the success of treatment of paediatric cancer have come, in part, from the high participation rate of patients in such studies. The present article reviews the definitions and goals of phase 1, 2 and 3 trials. A known and trusted physician or paediatrician can be helpful in conjunction with the oncologist in guiding patients and their families and helping them understand the risks and benefits of participation in clinical trials.