Traditionally, it has been assumed that intellectual development in children with growth hormone deficiency (GHD) is distributed between ranges of a normal population based on the observation that it does not differ substantially from that of children of the same age. Nevertheless, few studies have investigated this assumption. This Spanish Collaborative study was prospectively planned with two main purposes: to study a possible influence of GHD on intelligence quotient (IQ), personality traits and adaptative capacity and to study the evolution of these parameters during substitution therapy with growth hormone (GH). Although the overall intellectual ability of children with GHD is comparable to that of a normal reference population, some areas such the motor-component scale (evaluated by McCarthy test) and performance IQ (evaluated by WISC-R) were below the mean at the beginning of the study, showing significant improvement during therapy. Emotional adjustment (normal at study start) also improved significantly during treatment. Females showed better adjustment capacity before and during GH therapy. Longer studies with an increased number of cases are needed to confirm these effects of GHD and its treatment in children.