The aim of this work was to evaluate the psychometric properties of the Numerical Rating Scale-11 (NRS-11) when used to assess pediatric pain intensity. We performed two studies: 175 schoolchildren, aged 8-12, participated in Study 1 and 63 children undergoing surgery and aged 6-16, participated in Study 2. The NRS-11 showed (a) adequate convergent construct validity when correlated with the Faces Pain Scale - Revised (FPS-R; r(1)=0.78, r(2)=0.93); (b) adequate discriminant validity in relation to measures of pain-related affect (z(1)=3.55, z(2)=7.62) and disability (z(1)=7.62, z(2)=6.83); and (c) adequate criterion-related validity using measures of pain-related affect (r(1)=.58, r(2)=.66), disability (r(1)=0.22, r(2)=.39), and quality of life (r(2)=-.46). Schoolchildren were asked whether they preferred using the NRS-11 or the FPS-R when reporting the intensity of their pain. While both sexes and both the younger and older age groups preferred the FPS-R, this preference was more marked among girls and younger children. The NRS-11 has shown an acceptable level of validity for assessing pain intensity in both samples, however, additional research is needed in order to fully clarify the lower age limit in which the NRS-11 can be used.