It is conceivable that the processes involved in embryogenesis and early development of the nervous system could be affected in some way so as to contribute to the degradation seen in nervous system degeneration. As we further our understanding of the underlying mechanisms of these two processes individually, we find that it is indeed the case that there are some overlaps. Here, one particular molecule, apolipoprotein E is discussed. The actions of this molecule are fundamental to brain development, and recent work has uncovered a link between the ?4 allele and the onset and development of Alzheimers disease, the major cause of dementia in the elderly. This review will present the current lines of thought as to how apoE and its receptors modulate brain development, and how these processes may contribute to the development of the underlying pathology of Alzheimers disease.