Faces scales have become the most popular approach to eliciting children's self-reports of pain, although different formats are available. The present study examined: (a) the potential for bias in children's self-reported ratings of clinical pain when using scales with smiling rather than neutral 'no pain' faces; (b) levels of agreement between child and parent reports of pain using different faces scales; and (c) preferences for scales by children and parents. Participants were 75 children between the ages of 5 and 12 years undergoing venepuncture, and their parents. Following venepuncture, children and parents independently rated the child's pain using five different randomly presented faces scales and indicated which of the scales they preferred and why. Children's ratings across scales were very highly correlated; however, they rated significantly more pain when using scales with a smiling rather than a neutral 'no pain' face. Girls reported significantly greater levels of pain than boys, regardless of scale type. There were no age differences in children's pain reports. Parents' ratings across scales were also highly correlated; however, parents also had higher pain ratings using scales with smiling 'no pain' faces. The level of agreement between child and parent reports of pain was low and did not vary as a function of the scale type used; parents overestimated their children's pain using all five scales. Children and parents preferred scales that they perceived to be happy and cartoon-like. The results of this study indicate that subtle variations in the format of faces scales do influence children's and parents' ratings of pain in clinical settings.