© 2015 Elsevier Inc. The original norms for the Revised Infant Temperament Questionnaire (RITQ) were published in 1978 and were based on a small sample from the US. The aim of this study is to compare temperament scores from the original RITQ against scores from a large population-based cohort of infants from the UK. This study consists of 10,937 infants from the Avon Longitudinal Study of Parents and Children (ALSPAC) born between April 1991 and December 1992 in the southwest of England. Infant temperament at 6 months of age was reported by parents using the adapted RITQ. Responses were scored according to the RITQ manual and then categorized into temperament groups (easy, intermediate low, intermediate high, and difficult) using either the RITQ norms or norms derived from the data. The scores for each temperament subscale and the proportion of children in each temperament group were compared across the two methods. Subscale scores for the ALSPAC sample were higher (more "difficult") than the RITQ norms for rhythmicity, approach, adaptability, intensity, and distractibility. When RITQ norms were applied, 24% infants were categorized as difficult and 25% as easy, compared with 15% difficult and 38% easy when ALSPAC norms were used. There are discrepancies between RITQ norms and the ALSPAC norms which resulted in differences in the distribution of temperament groups. There is a need to re-examine RITQ norms and categorization for use in primary care practice and contemporary population-based studies.