The aim of this paper was to describe the development of the cognitive domain of the Preschool Developmental Assessment Scale (PDAS) for assessment of preschool children with developmental disabilities. The initial version of the cognitive domain consisted of 87 items. They were administered to 324 preschool children, including 240 children from preschools and 84 children with developmental disabilities. Initial Rasch analysis results indicated that the fit statistics of 42 of the items were outside the acceptable range. Based on the fit statistics and considering the overall structure of the scale, the revised version consisted of 40 items and this version conformed to the Rasch expectations. The revised 40-item scale could differentiate between children with typical development and children with developmental disabilities. It could also differentiate between children from different age groups. The internal consistency estimate (KR-20) was 0.93. The cognitive domain of the PDAS is considered a promising developmental assessment tool for assessment of developmental disabilities. (Contains 1 figure and 2 tables.)