Age and sex differences were investigated in children's self-report of venipuncture pain. Equal numbers of boys and girls aged 3-15 years (n=110) made separate ratings of the intensity and unpleasantness of their needle pain, using a paired Visual Analogue Scale (VAS) technique. The parents of these children used the same method to give ratings of predicted pain and unpleasantness before the needle, as well as ratings based on observing their child during the needle. Results showed that, across age, children's intensity and unpleasantness scores were highly correlated (r=0.78), and that both of these ratings decreased with increasing age. Analyses of covariance showed that, with the variance in the unpleasantness ratings accounted for, a significant age main effect persisted for the intensity ratings (scores decreasing with increasing age), with no effect of sex. In the corollary analysis, with intensity scores entered as a covariate, unpleasantness ratings showed no main effect of age, but a significant main effect of sex emerged: girls' ratings of pain unpleasantness, when averaged across age, were significantly higher than boys'. The interaction between age and sex was explored in analysis of the relative difference between intensity and unpleasantness ratings. The results indicated that, from approximately 8-years of age, children (especially girls) gave significantly higher ratings of unpleasantness than sensory intensity of needle pain. Prior to the age of 8 years, children tended to give equivalent ratings of intensity and unpleasantness, with no evidence of a sex difference. The agreement between parental and children's ratings was higher for parents' observed, as opposed to predicted, scores, especially for pain intensity, with no systematic influence of the child's age and sex. In conclusion, it is suggested that age effects in children's self-report of needle pain are predominantly manifest in ratings of sensory intensity, whilst sex effects are predominantly manifest in ratings of an affective (unpleasantness) dimension. It is argued that both age and sex differences are largely the function of pain reporting variables, rather than reflecting fundamental age or sex based variance in nociceptive processing. Copyright (C) 1999 International Association for the Study of Pain. Published by Elsevier Science B.V.