Background: The Bayley Scales of Infant and Toddler Development, 3rd Edition (Bayley-III) is frequently used in international child development research. No studies examine its psychometric properties when culturally adapted within the Kenyan context.

Aims: To culturally adapt the Bayley-III for use in Kenya and evaluate its validity and reliability.

Methods and procedures: Forward and backward translation, cognitive interviews, and a brief pilot of culturally adapted items were performed. This psychometric study was part of another study on children born to mothers with HIV in Eldoret, Kenya. One hundred seventy-two children aged 18-36 months were assessed for cognition, receptive/expressive communication, and fine/gross motor domains using the Bayley-III. Confirmatory factor analysis (CFA), inter-scale Pearson correlations, internal consistency, t-tests, and test-retest reliability were performed.

Outcomes and results: The mean age of children was 22.8 (SD 4.5) months old; 52.7 % (n = 89) were male. CFA revealed that both two- and three-factor indices had good and comparable fit. Pearson correlations were high between fine motor and receptive communication (r >0.70). Internal consistency was very strong for all of the subtests, with Cronbach coefficient alpha scores ranging from 0.88 to 0.96. Known groups/convergent validity was confirmed with stunting and parental concern for delays. Test-retest reliability was good and did not differ substantially across groups.

Conclusions and implications: The Kenyan adapted Bayley-III is a psychometrically acceptable tool to assess child development. The scaled and composite scores should not be used to define Kenyan developmental norms, but it can be useful for comparing groups within research settings.