Abstract Background Attention and inhibition are core executive-function deficits in FRagile X syndrome (FXS). This pilot study evaluated the feasibility, reproducibility, and clinical relevance of the KiTAP, a computer-based pictorial measure of attention and inhibition with an enchanted-castle theme, in an FXS cohort. Methods The 8-subtest KiTAP battery (as many subtests as each could perform) was given to 36 subjects with FXS, of variable age and cognitive/behavioral functioning, and 29 were retested, with an interval of 2 to 4 weeks between sessions. Subjects were rated by parents on the Aberrant Behavior Checklist-Community Edition (ABC-C) and Behavior Assessment System for Children, Second Edition (BASC-2). Feasibility, ceiling and basal effects, and data range and distribution analyses were used to eliminate outliers and invalid data points. Reproducibility of scores was analyzed using intraclass correlation coefficients (ICCs) and validity/clinical relevance was assessed by correlating KiTAP scores with ABC-C and BASC-2 scores. Results Most of the participants with FXS were able to complete the Alertness, Distractibility, Flexibility, and Go/NoGo subtests.About 50 to 60% completed the Visual Scanning and Vigilance subtests, and 20 to 25% completed the Sustained Attention and Divided Attention subtests. A panel of seven scores from four subtests were identified as feasible for most subjects, lacked excessive ceiling, basal, or learning effects, exhibited an acceptable range and distribution of scores, had good reproducibility (ICC > 0.7), and correlated with behavioral ratings for hyperactivity or attention (P < 0.01). Only minor differences in performance on the KiTAP were seen between mental age-matched cohorts of subjects with FXS and non-FXS intellectual disability. Conclusions The KiTAP can be administered to cohorts with FXS over a wide range of function with valid reproducible scores. With additional validation, it could represent a useful outcome measure for assessment of attention/executive-function abilities in clinical trials targeted to these core deficits in FXS.