In this paper, different means of assessing cognitive development in children with severe impairments in "both" their expressive language and their motor skills are reviewed. A range of techniques are considered, including traditional cognitive tests and behavioral and physiological measures, but these techniques are generally impractical and minimally informative when it comes to assessing children with both motor and speech impairments. Electrophysiological measures show some promise for the future, but are currently inadequate for wide-ranging cognitive assessment. Development of the Carter Neurocognitive Assessment (CNA) is described. The CNA is appropriate for use in clinical and research settings and was designed to minimalize the impact of severely impaired motor skills and expressive language on performance. The CNA is intended to itemize and quantify a range of skills reflecting a cognitive level up to approximately 18 to 24 months in four areas: Social Awareness, Visual Attention, Auditory Comprehension and Vocal Communication. The use of the CNA to assess the performance and developmental growth of eight children with Holoprosencephaly (HPE), a midline developmental brain malformation, is described. The CNA is a useful tool for the assessment of children with severely compromised motor and verbal skills and has provided a more positive view of the cognitive potential of children with severe handicaps, such as the sample of children with HPE, than that presented in the past.