Although adaptive behavior became a diagnostic criterion in the 5th edition of the American Association on Intellectual and Developmental Disabilities, AAIDD (Heber, 1959, 1961), there are no measures with adequate psychometric properties for diagnosing significant limitations in adaptive behavior according to the current conception of the construct. This fact has led to an excessive reliance on intellectual functioning measures. The goal of the present paper consists of presenting the development of the AAIDD's forthcoming Diagnostic Adaptive Behavior Scale (DABS) in Spain, and, specifically, it will be focused on one of its three forms: DABS Form 4-8 years old. The sample consisted of 388 people, aged 4-8 years old, with and without intellectual disabilities. The functioning of an initial pool of 168 items was analyzed under the assumptions of Item Response Theory models (IRT) with the aim to select those items around the cut-off point for determining significant limitations in adaptive behavior. A set of 72 items was selected (96 items were removed due to misfit, unsatisfying response category functioning, or low precision of measurement). The final version seems to be essentially unidimensional, shows good fit to the model, and represents an accurate precision of measurement around the cutoff point for diagnosing significant limitations in conceptual, social or practical skills. (Contains 3 figures and 2 tables.)