Objective To determine the intra-rater and inter-rater reliability of the Sexual Knowledge Picture Instrument (SKPI), a potential diagnostic instrument for young suspected victims of sexual abuse containing three scoring forms, that is, verbal responses, non-verbal reactions and red flags. Design Video-recorded SKPI interviews with children with and without suspicion of child sexual abuse were observed and scored by two trained, independent raters. The second rater repeated the assessment 6 weeks after initial rating to evaluate for intra-rater reliability. Subjects 78 children aged 3-9 years old were included in the study. 39 of those included had known suspicion of sexual abuse and the other 39 had no suspicion. Main outcome measures Intra-rater and inter-rater reliability of the scores per study group and in the total sample were assessed by Cohen's kappa and percentage of agreement (POA). Results The median intra-rater Cohen's kappa exceeded 0.90 and the POA exceeded 95 for all three forms in both study groups, except for the red flag form (median Cohen's kappa 0.54 and POA 87 in the suspected group, and 0.84 and 92, respectively, in the total sample). For the verbal scoring form the median inter-rater Cohen's kappa and POA were 1.00 and 100, respectively, in both groups. For the non-verbal form the median inter-rater kappa and POA were 0.37 and 97, respectively, in the suspected group, and 0.47 and 100, respectively, in the control group. For the red flag form, they were 0.37 and 76, respectively, in the suspected group and 0.42 and 77, respectively, in the control group. Conclusion The reliability of the SKPI verbal form was sufficient, but there is room for improvement in the non-verbal and red flag scoring forms. These forms may be improved by adjusting the manual and improving rater training.